I  ftMSAmSIflSU^BM.  SURVEY 


3  3051  00006  8746 


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STATE  OF  ILLINOIS 

STATE  GEOLOGICAL  SURVEY 

FRANK  W.   DeWOLF,   Director 


Monograph  1 


The 


Mississippian  Brachiopoda 


OF  THE 


Mississippi  Valley  Basin 


Text 


BY 


STUART  WELLER 


ILLINOIS  STATfc 
GEOLOGICAL  SURVEY 


ILLINOIS  STATE  GEOLOGICAL  SURVEY 

UNIVERSITY  OF  ILLINOIS 

URBANA 

1914 


Jeffersons  Printing  Company 
Springfield,  III. 


REPORT  PUBLISHED  UNDER  STATE  GEOLOGICAL  COMMISSION 

Edward  F.  Dunne,  Chairman 
Governor  of  Illinois 

Thomas  C.  Chamberlin,  Vice-Chairman 

Edmund  J.  James,  Secretary 
President  of  the  University  of  Illinois 


Frank  W.  DeWolf,  Director 


REPORT  PREPARED  UNDER  STATE  GEOLOGICAL  COMMISSION 

Charles  S.  Deneen,  Chairman 
Governor  of  Illinois 

Thomas  C.  Chamberlin,  Vice-Chair  man 

Edmund  J.  James,  Secretary 
President  of  the  University  of  Illinois 


l^-AP-' 


CONTENTS 


Page 

Preface    9 

Geological   introduction 12 

Descriptions  of  genera  and  species 31 

Lingula 33 

Glossina  37 

Orbiculoidea  39 

Crania   43 

Leptsena   48 

Schuchertella   53 

Schellwienella    59 

Streptorhynchus    68 

Orthotetes  74 

Chonetes    78 

Chonopectus   95 

Productella   97 

Productus    103 

Diaphragmus   135 

Echinoconchus  138 

Strophalosia   143 

Rhipidomella  147 

Schizophoria    161 

Camarophoria    169 

-  Camarotoechia   175 

Liorhynchus    185 

Paryphorhynchus    187 

Pugnoides    192 

Allorhynchus  197 

Pugnax  202 

Rhynchotetra   205 

Tetracamera 212 

Shumardella 221 

Rhynchopora    227 

Centronella  241 

Selenella    243 

Trigeria    245 

Centronelloidea   246 

Cransena 248 

Dielasmoides    253 

Dielasma 256 

Girtyella   271 

Dielasmella  279 


b  CONTENTS 

Page 

1 1  a  mburgia    282 

Atrypa  284 

Cyrtina    286 

Spiriferina    291 

1  )elthyris    300 

Spirifer 307 

Brachythyris 370 

Cyrtia   382 

Syringothyrjs    384 

Pseudosyrinx 404 

Spiriferella    412 

Acanthospira    418 

Martinia 420 

Amhocoelia 423 

Reticularia    427 

Ptychospira    435 

Eumetria    437 

Acambona    448 

Hustedia   451 

Nucleospira 453 

Camarophorella   458 

Rowleyella    462 

Athyris   464 

Cliothyridina   472 

Composita   484 


LETTER  OF  TRANSMITTAL 


State  Geological  Survey 

University  op  Illinois,  February  15,  1913. 

Governor  E.  F.  Dunne,  Chairman,  and  Members  of  the  Geological  Survey 
Commission  : 

Gentlemen  :  When  the  present  Survey  was  created  in  1905  the  Geolog- 
ical Commission  adopted  a  balanced  program  which  emphasized  economic 
work  of  immediate,  though  perhaps  temporary,  value ;  it  nevertheless 
included  deep  scientific  research  into  fundamental  problems,  having  only 
indirect  bearing  on  economic  geology  of  the  State. 

The  Survey  has  now  published  nineteen  bulletins  and  many  useful  maps 
which  have  served  an  increasing  public  demand.  Nine  other  reports  are 
in  manuscript  form  for  early  printing.  I  now  have  the  pleasure  of  trans- 
mitting to  you  an  illustrated  report  on  the  Mississippian  Brachiopoda, 
by  Professor  Stuart  Weller  of  the  University  of  Chicago,  and  I  recommend 
that  it  be  published  as  the  first  of  the  scientific  monographs  of  the  Survey. 

Because  of  the  highly  technical  character  of  this  report  it  is  perhaps 
fitting  to  state  that  an  understanding  of  our  geological  formations  is  based 
not  only  on  their  materials  but  also  on  their  included  fossil  remains, 
which  indicate  the  relative  time-periods  during  which  the  rocks  were 
deposited.  The  Mississippian  formations  have  their  type  localities  in 
Illinois  and  the  immediately  adjoining  states  of  the  Mississippi  Valley. 
The  study  of  these  strata  for  more  than  half  a  century  has  been  attended 
by  considerable  confusion.  Professor  Weller 's  work,  extending  over  a 
period  of  eight  years,  has  solved  many  of  the  difficulties  of  stratigraphy 
and  paleontology.  His  monograph  will  be  gratefully  received  by  profes- 
sional geologists  throughout  the  world. 

Very  respectfully, 

Frank  W.  DeWolf,  Director. 


PREFACE 

No  comprehensive  study  of  the  fossils  of  the  Mississippian  formations 
of  Illinois  and  the  adjacent  parts  of  the  Mississippi  Valley  Basin  has  ever 
been  attempted.  The  species  have  been  described  in  various  publications, 
in  state  reports,  in  short  papers  in  the  transactions  of  learned  societies, 
geological  journals,  etc. ;  many  forms  have  never  been  illustrated,  and 
many  still  remain  undescribed.  The  literature  on  the  subject  is  widely 
scattered,  and  most  of  it  is  not  readily  accessible  to  a  large  number  of 
geological  workers  and  students.  James  Hall's  Report  on  the  Paleontol- 
ogy of  Iowa,  published  in  1858  and  long  since  out  of  print,  still  remains 
the  principal  source  of  information  to  most  students,  concerning  these 
faunas. 

The  present  work  is  a  start  towards  the  preparation  of  a  series  of 
monographs  which  it  is  hoped  may  eventually  cover  all  the  groups  of 
organisms  whose  fossil  remains  are  preserved  in  these  formations.  The 
brachiopods  have  been  selected  as  the  first  group  to  receive  consideration 
because  of  their  almost  universal  presence  in  the  faunas,  and  because  their 
characters  are  such  as  to  make  them  most  readily  recognizable  under 
ordinary  conditions.  The  specimens  are  much  more  apt  to  be  preserved 
in  a  sufficiently  complete  condition  to  allow  of  their  identification,  than 
are  the  specimens  of  some  other  groups,  such  as  the  crinoids  for  instance. 
They  are  much  more  abundant  than  are  the  species  of  the  several  classes 
of  Mollusca,  and  they  do  not  require  the  grinding  of  thin  sections,  as  do 
many  of  the  Bryozoa.  Furthermore  the  species  are  almost  all  rather 
closely  limited  in  their  geological  range,  being  characteristic  for  the  most 
part,  of  the  fauna  in  which  they  occur.  The  field  geologist  who  has  the 
means  at  hand  to  enable  him  to  recognize  the  brachiopods  will  not  have 
difficulty  in  determining  the  horizon  of  the  strata  he  may  be  studying. 

In  the  present  work  all  the  brachiopods  known  to  occur  in  the  forma- 
tions of  the  standard  Mississippian  section  of  the  Mississippi  Valley,  so 
far  as  they  could  be  secured,  have  been  considered.  These  formations 
have  their  typical  development  not  alone  in  Illinois,  but  also  in  Missouri 
and  Iowa,  so  that  not  a  few  of  the  examples  studied,  described,  and  illus- 
trated are  from  localities  outside  of  Illinois,  although  most  of  the  species 
may  be  looked  for  in  the  Illinois  formations.  A  few  forms  from  adjacent 
regions,  Indiana,  Kentucky,  Arkansas,  and  southwestern  Missouri  have 
been  included  in  the  discussion  of  the  species  and  perhaps  may  never  be 
found  in  any  Illinois  locality ;  the  reason  for  their  inclusion  here  being 
their  relationship  to  Illinois  species. 


10  m  ississil'l'l AN    BRACHIOPODA 

Under  the  discussion  of  each  species  the  name  of  the  geological  forma- 
tion or  formations  of  whose  fauna  the  species  is  a  member,  has  been 
recorded,  bu1  ao  attempl  has  been  made  to  record  all  the  localities  from 
which  the  species  is  known.  Iii  the  explanation  of  the  plates,  however. 
the  exact  Locality  of  the  specimen  illustrated  has  always  been  mentioned. 

The  material  used  in  the  preparation  of  the  reporl  lias  been  drawn  from 
all  available  sources.  The  collections  in  the  Walker  Museum  of  The  Uni- 
versity of  Chicago  have  been    a    niosl  prolific  source  of  supply  because  of 

the  presence  of  the  Gurley  collection  and  the  James  Ball  collection,  both 
of  which  are  rich  in  types  of  I\l ississippian  fossils,  as  well  as  of  several 
smaller  collections,  of  which  the  Sampson  collection  and  the  Van  Home 
collection  especially  have  supplied  important  specimens.  Through  the 
kindness  of  Dr.  A.  R.  Crook,  curator  of  the  Illinois  State  Museum  of  Nat- 
ural History,  several  type  specimens  have  been  loaned  for  study  and  illus- 
tration from  the  collections  of  that  institution.  Dr.  E.  0.  Hovey  of  the 
American  Museum  of  Natural  History  in  New  York  City  has  been  most 
generous  in  his  willingness  to  send  many  important  type  specimens  to  the 
author  for  study  and  illustration.  The  many  types  of  species  described 
by  Winched  and  by  White  and  Whitfield,  preserved  in  the  White  collec- 
tion in  the  museum  of  the  University  of  Michigan,  have  been  made  avail- 
able for  study  and  illustration  through  the  co-operation  of  Dr.  B.  C.  Case. 
Dr.  R.  S.  Bassler  has  generously  loaned  certain  material  from  the  U.  S. 
National  .Museum  in  Washington.  Besides  these  curators  of  great  public 
collections,  private  collectors  have  not  been  backward  in  furthering  the 
preparation  of  the  report.  Prof.  R.  R.  Rowley,  of  Louisiana,  Missouri, 
who  has  described  many  species  of  Mississippian  brachiopods,  has  gener- 
ously placed  in  the  hands  of  the  writer  either  the  types  or  authentic  speci- 
mens of  all  his  species,  which  have  been  used  for  the  illustrations  and  as 
the  basis  for  the  definitions  here  published.  Mr.  D.  K.  Greger  of  Fulton, 
Missouri,  has  made  his  extensive  collection  of  Mississippian  brachiopods 
freely  available  to  the  writer  in  the  preparation  of  the  report.  To  all 
these  curators  and  collectors  I  wish  to  express  my  great  obligation,  for 
without  their  co-operation  the  report  could  never  have  been  made  as  com- 
plete as  it  now  is. 

No  claim  of  absolute  completeness  can  be  made  for  any  work  of  this 
sort.  Many  species  were  described  entirely  without  illustrations  by 
earlier  workers  in  the  subject,  and  in  many  instances  the  original  types  of 
these  species  have  been  lost  or  destroyed.  It  has  been  possible  to  recog- 
nize many  such  species  from  the  definitions  or  from  the  definitions  along 
with  specimens  more  recently  collected  in  the  original  localities,  but  there 
still  remains  a  considerable  number  of  such  species  which  have  not  been 
recognized,  some  or  all  of  which  may  still  be  cleared  up  through  future 
collection  and  study.  It  is  also  to  be  expected  that  further  work  in  the 
field  may  bring  to  light  additional  undescribed  species. 


PREFACE  11 

In  the  preparation  of  the  body  of  the  report  new  definitions  of  all  of  the 
species  have  been  written  so  that  the  usage  of  terms  is  uniform  through- 
out. In  the  definitions,  the  usual  size  of  the  members  of  any  species  has 
been  expressed  in  the  relative  terms  large,  small,  etc.,  these  terms  being 
used  on  the  arbitrary  basis  that  a  specimen  having  a  diameter  of  about  25 
mm.  or  1  inch,  is  medium  sized.  Specimens  smaller  than  this  are  below 
medium  size  or  small,  while  specimens  of  larger  dimensions  are  above 
medium  size  or  large.  Besides  these  general  dimensions,  accurate  meas- 
urements of  one  or  more  specimens  have  always  been  given.  The  usage  of 
the  terms  cast  and  mould  is  not  entirely  uniform  among  paleontological 
writers.  In  the  present  work  the  term  internal  cast,  or  cast,  of  the  in- 
terior of  the  shell,  is  applied  to  the  hardened  matrix  which  has  filled  the 
interior  of  the  shell  or  valve,  the  cavity  of  the  shell  or  valve  being  as- 
sumed to  be  the  mould  in  which  such  a  cast  was  formed. 

All  the  illustrations  on  the  accompanying  plates  are  reproduced  from 
photographs  taken  from  the  actual  specimens.  During  the  earlier  part  of 
the  work  I  was  materially  assisted  in  the  preparation  of  photographs  by 
Mr.  J.  M.  Jessup,  and  I  wish  here  to  acknowledge  his  very  efficient  aid  in 
this  part  of  the  work. 

Stuart  Welder. 
Chicago,  September  1,  1913. 


GEOLOGICAL  INTRODUCTION 

The  Mississippian  section  in  Illinois  and  the  adjacent  portions  of  the 
Mississippi  Valley  Basin  constitutes  the  typical  section  of  that  system  of 
strata  in  America.  The  entire  series  of  formations  is  prevailingly  cal- 
careous from  its  base  to  above  the  middle,  but  the  upper  portion  includes 
conspicuous  sandstone  strata  interbedded  with  important  shales  and  lime- 
stones. The  name  "Snbearboniferous  limestone"  was  first  used  by  Owen 
for  this  series  of  formations  and  was  the  common  designation  for  these 
rocks  until  1891,  at  which  time  Williams1  proposed  to  subdivide  the  Car- 
boniferous into  the  Mississippian  and  the  Pennsylvanian,  the  former  name 
being  applied  to  the  so-called  Subcarboniferous  rocks  of  earlier  authors, 
and  the  latter  to  the  series  of  formation  which  had  previously  been  desig- 
nated as  Coal  Measures.  These  two  names  were  at  once  generally  adopted 
by  American  geologists. 

The  subdivision  of  the  entire  Mississippian  system,  with  the  application 
of  geographic  formation  names  to  the  several  units,  in  accordance  with 
modern  usage,  was  first  accomplished  by  James  Hall  in  his  Iowa  Report2 
in  1858,  although  formation  names,  mostly  of  lithological  or  paleontologi- 
cal  derivation,  had  been  applied  to  the  several  formations  by  earlier 
authors.  In  his  study  of  the  section  Hall  had  as  an  assistant  Mr.  A.  H. 
Worthen,  who  later  became  the  state  geologist  of  Illinois,  and  who  used 
Hall's  nomenclature,  with  some  minor  changes,  in  his  reports  on  the 
geology  and  paleontology  of  Illinois.  These  names,  used  by  Hall  and  by 
Worthen,  have  become  standard  in  the  typical  Mississippian  section,  al- 
though later,  more  detailed  and  more  critical  studies  have  necessitated 
certain  important  changes  in  the  interpretation  of  the  section,  and  the 
introduction  of  additional  formation  names.  Future  studies  may  necessi- 
tate other  changes  in  the  classification  and  nomenclature  of  the  beds. 

The  classification  of  the  Mississippian  system  here  recognized  is  as 
follows : 

CLASSIFICATION  OF  THE  MISSISSIPPIAN  SYSTEM 

V.     Chester  group. 

Clore  formation. 
Palestine  formation. 
Menard  formation. 
Okaw  formation. 
Ruma  formation. 
Paint  Creek  formation. 

1  Bull.  U.  S.  Geol.  Survey  No.  80.     (1891.) 

2  Report  on  the  Geological  Survey  of  the  State  of  Iowa,  vol.  1,  Pts.  1  and  2.  (1858.) 


GEOLOGICAL   INTRODUCTION  13 

Yankeetown  formation. 

Renault  formation. 

Brewerville  sandstone. 
IV.     Ste.  Genevieve  limestone. 
III.     Meramec  group. 

St.  Louis  limestone. 

Salem  limestone. 
II.     Osage  group. 

Warsaw  formation. 

Keokuk  limestone. 

Burlington  limestone. 
I.     Kinderhook  group. 

Containing  many    formations  more    or    less    local   in   their 
geographical  distribution. 

I.     KINDERHOOK  GROUP 

The  lowermost  formations  of  Mississippian  age,  constituting  the  Kinder- 
hook  group,  were  correlated  by  Hall  with  the  Chemung  formation  of  the 
New  York  Devonian  section,  but  they  are  now  universally  considered  to  be 
of  younger  age,  and  to  constitute  the  initial  group  of  formations  in  the 
Mississippian  system.  The  Kinderhook  formations  are  exceedingly  variable 
in  their  development  in  different  parts  of  the  Mississippi  Basin,  including 
limestone,  sandstone,  and  shale  formations.  The  sections  lack  uniformity 
in  any  two  localities  separated  by  a  considerable  distance ;  and  the  faunas 
show  much  variation  in  the  several  formations  and  in  different  regions. 

At  the  locality  from  which  the  name  of  the  group  was  derived,  Kinder- 
hook,  Pike  County,  Illinois,  the  following  section  may  be  seen : 

SECTION  AT  KINDERHOOK,  ILLINOIS 

Osage  group. 

4.  Burlington  limestone. 

Kinderhook  group.  Feet 

3.     Thin-bedded,    fine-grained   limestone 6 

2.     Thin-bedded  sandstone  and  sandy  shales 36 

1.     Argillaceous  and  sandy  shales,  partly  hidden 40 

Another  locality  considered  as  typical  by  Meek  and  Worthen,  who  first 
used  the  name  Kinderhook  group,  is  that  exposed  in  the  neighborhood  of 
Burlington,  Iowa,  where  the  following  succession  of  beds  may  be  studied : 

SECTION  AT  BURLINGTON,  IOWA 

Osage  group. 

8.     Burlington  limestone. 

Kinderhook  group.  Feet 

7.     Soft,  buff,  dolomitic  limestone 3-5 

6.     White,  oolitic  limestone 2-4 

5.  Fine-grained,  yellow  sandstone 6-7 


14  m  ississil'l'l  AN    BRACHIOPODA 

Feet 
4.     Compact,  much-fractured,  gray  limestone 12-18 

3.  Thin  band  of  hard,  impure  limestone,  filled  with  Chonetes, 

often  associated  with  a  thin  oolitic  band y2-l 

2.  Soft,  Eriable,  argillaceous  sandstone,  usually  yellow,  but 

Locally  harder  and  bluish,  with  a  large  fauna  of  which 
Chonopcctus  fischeri  is  the  most  conspicuous  species. 
The  Chonopectus  sandstone 25 

1.  Soft,  blue,  argillaceous  shale  ( exposed) 60 

At  Hannibal,  Louisiana,  and  Clarksville,  Missouri,  the  section  is  as  fol- 
lows : 

SECTIONS   AT  MISSOURI  LOCALITIES 

Osage  group. 

4.  Burlington  limestone. 

Kinderhook  group.  Feet 

3.  Fine-grained,  compact,  buff  limestone 10-15 

2.  "Vermicular  sandstone  and  shale"  (Hannibal  sandstone)       70 

1.  Compact,  blue-gray  limestone  with  lithographic  texture 

(Louisiana  limestone)    60 

At  Hamburg,  Calhoun  County,  Illinois,  the  section  is  similar  to  that  at 
Louisiana,  Missouri,  except  in  the  notable  reduction  in  thickness  of  the 
Louisiana  limestone,  and  the  introduction  of  an  oolitic  limestone  above 
the  Louisiana.     The  section  is  as  follows: 

SECTION   AT    HAMBURG,    ILLINOIS 

Osage  group. 

5.  Burlington  limestone. 

Kinderhook  group.  Feet 

4.  "Vermicular  sandstone  and  shale"  (Hannibal  sandstone 

and  shale)    (?) 

3.  White  to  yellow  or  flesh-colored  oolitic  limestone,  with  in- 

terbedded  layers  of  sandy  shales  (Hamburg  oolite) .  .  .  1-15 

2.  Brown,  sandy  shale 1-8 

1.     Compact,     gray     limestone     with     lithographic     texture 

(Louisiana  limestone)    5 

In  central  Missouri  the  entire  Kinderhook  is  represented  in  the  Chou- 
teau limestone,  about  100  feet  in  thickness. 

In  southwestern  Missouri  the  Kinderhook  section  is  made  up  of  three 
members,  as  follows: 

SECTION  IN  SOUTHWESTERN  MISSOURI 

Osage  group. 

4.  Burlington  limestone. 

Kinderhook  group.  Feet 

3.  Buff-colored  limestone    (Pierson   limestone) 30 


GEOLOGICAL   INTRODUCTION  15 

Feet 

2.  "Vermicular"     sandstone     with      accompanying     shales 

(Northview  sandstone  ),  about , 60 

1.  Tough,  bluish-gray,  granular  limestone   (Chouteau  lime- 

stone, lower  part),  about 20 

In  Jefferson  County,  Missouri,  25  miles  below  St.  Louis,  the  Kinderhook 
section  is  as  follows  : 

SECTION  IN  JEFFERSON  COUNTY,  MISSOURI 

Osage  group. 

5.     Burlington  limestone. 
Kinderhook  group.  Feet 

4.     Red  to  green,  cherty  limestone,  often  very  argillaceous, 

(Fern  Glen  formation) 30 

3.  Fine-grained,  yellow  or  brown  sandstone  (Bushberg  sand- 

stone)         14 

2.  Sandy  shale    Ms 

1.  Gray  or  yellowish  oolitic  limestone  (Glen  Park  limestone). 

about 1 

In  Union  County,  Illinois,  in  the  W.  y2  sec.  11,  T.  12  S.,  R.  2  W., 
about  3V2  miles  northwest  of  Jonesboro,  along  the  creek  west  of  the 
M.  &  0.  Railroad  track,  the  Kinderhook  has  a  very  different  expression 
from  that  at  any  of  the  points  further  north,  as  follows : 

SECTION  3]/2  MILES  NORTHWEST  OF  JONESBORO,  ILLINOIS. 

Osage  group. 

4.  Burlington  limestone. 

Kinderhook  group.  Feet 

3.  Green,  brittle  shale 40 

2.  Impure,  nodular  limestone  ( ?Rockford  limestone) 1 

Devonian. 

1.  Thinly  laminated,  black,  brittle,  shale,  (Chattanooga  shale)  .  . 
These  sections  Avill  suffice  to  exhibit  the  variable  character  of  the  Kin- 
derhook sediments.  Some  of  the  formations,  as  noted  above,  have  already 
been  given  local  formation  names,  and  others  will  doubtless  be  named  in 
the  future,  but  in  no  case  can  any  formational  unit  be  traced  continuously 
throughout  the  entire  basin.  In  the  central  portion  of  the  basin  the  Kin- 
derhook sediments  invariably  rest  unconformably  upon  subjacent  strata, 
but  in  the  more  northern  region,  as  at  Burlington,  Iowa,  and  in  the  more 
southern  region,  as  in  Union  County,  Illinois,  it  is  not  improbable  that  the 
sedimentation  was  continuous  from  the  preceding  Upper  Devonian  into 
the  Kinderhook.  It  is  believed  that  in  early  Kinderhook  time  two  distinct 
basins  in  the  Mississippi  Valley  were  occupied  by  the  sea,  one  to  the  north 
and  another  to  the  south  of  a  land  barrier,  because  the  faunas  of  these 


lti  Mlssissil'l'lAN   BRACHIOPODA 

two  basins  are  fundamentally  different  in  composition  and  origin.  With 
the  progress  of  Kinderhook  time  lliis  land  barrier  was  gradually  sub- 
merged,  causing  the  borders  of  the  seas  upon  the  two  sides  to  approach 
each  other,  until  in  late  Kinderhook  time  the  northern  and  southern  seas 
joined,  and  the  fauna  from  the  southern  sea  spread  into  the  northern 
basin,  supplanting  the  previously  existing  fauna  of  that  region. 

II.     OS  AG?]  GROUP 

The  formations  constituting  the  Osage  group  are  very  different  from 
those  of  the  Kinderhook  in  that  they  arc  fairly  uniform  in  both  lithological 
and  faunal  character,  and  can  be  traced  through  the  entire  Mississippi 
Basin.  The  formations  commonly  included  in  the  Osage  are  the  'Burling- 
ton limestone,  the  Keokuk  limestone,  and  the  Warsaw  formation.  Ulrich,1 
however,  includes  the  last  of  these  formations  in  the  superjacent  Meramee 
group,  and  considers  the  Fern  Glen  formation,  here  placed  in  the  Kinder- 
hook. as  a  basal  member  of  the  Osage. 

Burlington  Umestone. — The  Burlington  limestone  takes  its  name  from 
Burlington,  Iowa,  and  the  formation  has  its  most  typical  development  in 
the  southeastern  counties  of  Iowa  and  the  adjacent  portions  of  Illinois. 
Further  south  the  formation  is  continuously  exposed  in  the  Mississippi 
River  bluffs  from  Quincy  to  northern  Calhoun  County,  and  also  in  south- 
ern Jersey  County.  It  has  a  considerable  area  of  outcrop  in  the  river 
bluffs  and  elsewhere  in  Monroe  County,  and  still  further  south  in  Jackson 
and  Union  counties.  In  its  typical  development  in  southeastern  Iowa,  a 
total  thickness  of  about  150  feet  has  been  recorded  for  the  formation,2 
but  its  thickness  commonly  falls  short  of  this  and  in  some  localities  is  not 
over  100  feet.  The  formation  is  constituted  mainly  of  limestone  and  chert 
in  varying  proportions.  The  limestone  layers  are  conspicuously  crinoidal, 
generally  consisting  of  a  mass  of  the  separated  column  joints  and  plates, 
and  are  in  many  places  remarkably  pure,  locally  containing  98  per  cent 
of  calcium  carbonate.  In  Iowa  the  uppermost  30  feet  comprise  the  so- 
called  Montrose  chert  bed,  in  which  the  limestone  and  chert  occur  in 
alternate  horizontal  bands  a  few  inches  in  thickness,  the  chert  constituting 
50  per  cent  or  more  of  the  total  mass.  Elsewhere  in  the  formation  in  this 
region  the  chert  is  less  conspicuously  developed,  being  present  in  oc- 
casional horizontal  bands  or  in  horizontal  series  of  concretionary  nodules. 
Further  south  the  chert  is  not  so  conspicuously  concentrated  in  the  upper 
portion  of  the  formation,  but  in  many  places  occurs  abundantly  through- 
out the  entire  thickness,  or  elsewhere  more  concentrated  near  the  base. 

1TJ.  S.  Geol.  Survey,  Prof.  Paper,  36,  p.  24  (1905);  Bull.  Geol.  Soc.  America,  vol. 
22,  plate  29.     (1911.) 
2  Iowa  Geol.  Survey,  vol.  Ill,  plate  28,  opposite  p.  330.     (1895.) 


GEOLOGICAL    INTRODUCTION  17 

In  the  Monroe  County  exposures,  the  entire  thickness  of  the  formation  is 
made  up  largely  of  alternating  thin  bands  of  chert  and  limestone,  the 
chert  constituting  from  50  to  80  per  cent  of  the  total  mass.  In  Union 
County,  the  formation  is  more  cherty  below  and  contains  thick  beds  of 
pure  limestone  above. 

The  fauna  of  the  upper  beds  of  the  Burlington  limestone  is  remarkably 
uniform  throughout  the  entire  extent  of  the  formation,  and  consists 
largely  of  crinoids  and  brachiopods.  The  same  species  occur  from  Iowa  to 
southern  Illinois,  and  to  central  and  southwestern  Missouri.  The  faunas 
of  the  lower  beds  are  more  diverse  in  character,  and  in  many  localities 
contain  species  with  Kinderhook  affinities. 

Keokuk  limestone. — The  Keokuk  limestone  succeeds  the  Burlington  with 
perfect  conformity  in  those  sections  where  both  formations  are  present, 
and  in  places  it  is  difficult  to  draw  a  sharp  line  of  separation.  In  the 
neighborhood  of  Keokuk,  Iowa,  where  the  formation  is  typically  devel- 
oped, it  is  about  75  feet  thick,  a  measurement  which  perhaps  is  not  ex- 
ceeded elsewhere.  The  limestone  beds  of  the  formation  are  in  many 
places  more  or  less  argillaceous  and  are  separated  by  shaly  layers  which 
commonly  become  more  and  more  conspicuous  above,  and  locally,  as  in 
Monroe  County,  Illinois,  constitute  the  major  portion  of  the  entire  forma- 
tion. These  limestone  beds  are  prevailingly  bluish,  while  those  of  the 
Burlington  are  nearly  white,  or  towards  the  base  locally  brownish,  and 
the  chert  associated  with  the  Keokuk  limestone  is  darker  than  that  which 
is  commonly  present  in  the  Burlington. 

The  fauna  of  the  Keokuk,  like  that  of  the  Burlington,  is  largely  made 
up  of  crinoids  and  brachiopods,  but  in  addition  to  these  there  are  many 
bryozoans  in  the  shaly  beds,  and  some  horn  corals.  South  of  St.  Louis, 
especially  in  Monroe  and  Randolph  counties,  Illinois,  a  limestone  stratum 
near  the  very  top  of  the  formation  is  made  up  of  a  crowded  mass  of  the 
shells  of  the  large  Productus  magnus.  A  few  feet  above  this  Productus 
layer  is  another  limestone  bed  just  as  conspicuously  filled  with  the  shells 
of  a  species  of  Spirifer.  These  two  beds,  in  places  quite  separate,  and 
elsewhere  combined  in  a  single  layer,  mark  the  upper  limit  of  the  Keokuk 
formation  over  a  considerable  area  in  southwestern  Illinois  and  the 
adjacent  portion  of  Missouri. 

Warsaw  formation. — The  Warsaw  formation  is  typically  developed  at 
Warsaw,  Illinois,  where  it  attains  a  thickness  of  approximately  40  feet,1 
the  section  at  that  locality  being  as  follows: 

l  Bull.  Illinois  State  Geol.  Survey,  No.  8,  p.  84  (1907). 


18  .Mississii'i'iAX   BBACHIOPODA 

SECTION    AT    WARSAW,    ILLINOIS 

St.  Louis  limestone.  Pect 

11.     Dense,  bluish,  brecciated  Limestone 10 

Salem  limestone. 

10.  IMore  or  less  cross-bedded  limestone,  yellow  on  weathered 
surfaces  and  manular  in  appearance,  containing  large 
numbers  of  broken  bryozoans;  locally   replaced  by  a 

calcareous  gril    or  sandstone 8 

Warsaw  formation. 

9.  Thin  bedded  bluish  limestone,  interbedded  with  cal- 
careous shales.  Fossil  bryozoans  abundant,  especially 
TAoclema  punctata  and  Archimedes  wortheni 18 

8.      Fine  blue  shale 3 

7.     Hard,  light-colored  limestone,  with  few  poorly  preserved 

fossils 4 

6.     Fine  blue  shale 8 

5.     Magnesian   limestone   with   shaly   bands.     Fossils  poorly 

preserved  and  as  a  rule  rare,  mostly  bryozoans 8 

Keokuk  limestone. 

4.  Bluish  shales  with  numerous  geodes  which  are  generally 
smaller  than  those  in  the  magnesian  limestone  beds 
below 21 

3.     Magnesian  limestone  with  chert  bands 3 

2.  Magnesian  limestone  with  numerous  geodes.  Some  beds 
more  or  less  shaly.  Geodes  more  numerous  in  the 
middle  part  of  the  bed.  Fossils  poorly  preserved  and 
lather  rare,  mostly  imperfect  bryozoans 15 

1.  Blue  or  gray  crystalline  limestone  with  many  fossils. 
Thickness  not  known,  the  bed  extending  below  river 
level  (exposed)   15 

The  dominant  characteristic  of  the  Warsaw  formation  is  the  presence 
of  bluish  shale  with  subordinate  beds  of  limestone,  but  because  of  the 
softness  of  the  beds  they  are  rarely  well  exposed  at  the  surface.  The 
geographical  distribution  of  the  formation  follows  that  of  the  Keokuk 
limestone  wherever  the  full  thickness  of  that  formation  is  present  north 
of  the  latitude  of  St.  Louis.  The  formation  is  well  developed  in  the 
Meramec  basin  in  the  St.  Louis  quadrangle,  but  southward  it  is  seemingly 
absent,  allowing  the  superjacent  Salem  or  Spergen  limestone  to  rest 
directly  upon  the  Keokuk  formation.  For  example,  in  Monroe  County, 
Illinois,  almost  the  entire  Keokuk  formation  is  represented  by  shales, 
with  subordinate  bands  of  limestone,  which  closely  simulate  the  "Warsaw, 
but  the  upper  limit  of  these  beds  is  marked  by  a  conspicuous  limestone 
layer  from  one  to  several  feet  in  thickness,  which  is  crowded  with  speci- 
mens of  a  species  of  Spirifer.  In  the  Meramec  Highlands  section  in  the 
St.  Louis  quadrangle,  this  same  Spirifer  bed  occurs  about  50  feet  below 
the  base  of  the  Salem  limestone.  These  intervening  Warsaw  beds  are 
wanting  in  the  Monroe  County  section. 


GEOLOGICAL    INTRODUCTION  19 

In  his  classification  of  the  Mississippian,  Ulrich1  has  included  the 
Warsaw  with  the  succeeding  Salem  or  Spergen  and  St.  Louis  limestones 
in  the  Meramec  group.  This  grouping  of  the  formations  is  not  followed 
here  because  the  relationship  of  the  Warsaw  is  manifestly  closer  with  the 
subjacent  than  with  the  superjacent  formations.  Lithologically  there  is 
no  satisfactory  basis  for  differentiating  the  Warsaw  from  the  subjacent 
Keokuk,  and  the  faunal  relations  of  the  two  formations  are  very  close. 
In  the  typical  expression  of  the  two  formations  the  Keokuk  is  essentially 
limestone  with  subordinate  shale  beds,  while  the  Warsaw  is  largely  shale 
with  subordinate  limestone  beds ;  the  transition  from  one  formation  to 
the  other  being  gradual,  with  no  suggestion  of  an  unconformity.  The 
fauna  of  the  Warsaw  does  contain  an  element  which  is  closely  allied  to 
the  faunas  of  the  superjacent  formation,  but  this  fauna  is  notoriously  a 
recurrent  element  in  our  Mississippian  series,  occurring  also  well  down 
in  the  Keokuk,  in  the  St.  Louis  quadrangle  and  elsewhere.2  The  absence 
of  the  Warsaw  formation  south  of  St.  Louis  and  the  contact  of  the  Salem 
on  the  Keokuk,  indicates  a  line  of  unconformity  which  is  worthy  of  recog- 
nition as  a  line  of  major  subdivision  in  the  Mississippian  series.  Uncon- 
formable relations  between  the  thin  northern  extension  of  the  Salem  and 
the  subjacent  Warsaw  are  also  indicated  at  Warsaw,  Illinois.3 

III.     MERAMEC  GROUP 

The  Meramec  group  was  established  by  Ulrich1  to  include  the  Warsaw, 
"Spergen"  and  St.  Louis  formations,  but  in  the  present  report  it  is  used 
to  include  the  "Spergen"  or  Salem,  and  the  St.  Louis  limestones,  the 
Warsaw  formation  being  excluded  and  incorporated  in  the  Osage  group 
for  reasons  which  have  already  been  discussed.  In  the  older  reports  of 
the  Illinois  Survey,  by  Worthen,  this  series  of  limestones  was  commonly 
called  the  St.  Louis  group,  but  this  name,  although  proposed  many  years 
before  the  one  here  used,  is  inadvisable  because  the  use  of  the  same  name 
for  a  subordinate  formation  and  for  the  group  leads  to  much  confusion 
and  therefore  is  not  good  practice. 

Salem  limestone.*— The  Salem  limestone  has  its  typical  development  in 
Indiana  where  it  is  the  source  of  the  well-known  building  stone  which 
goes  on  the  market  as  "Bedford  Stone."     The  name  Bedford  limestone 

1U.  S.  Geol.  Survey,  Prof.  Paper,  No.  24,  p.  90  (1904);  U.  S.  Geol.  Survey,  Prof. 
Paper,  No.  36,  p.  24  (1905). 

2  Bull.  U.  S.  Geol.  Survey,  No.  438,  pp.  21  and  40  (1911). 

3  Bull.  111.  State  Geol.  Survey,  No.  8,  pp.  83-88  (1908). 

4  Spergen  limestone  of  Ulrich. 


I'll  MississilTl.W    BRACHIOPODA 

lias  been  used  for  the  formation,1  but  this  name  was  also  used  much  earlier 
and  is  still  in  use  for  a  formation  in  Ohio,  which  prior  use  makes  it 
unavailable  for  the  formation  here  under  consideration.  In  1901  Cumings2 
proposed  the  name  Salem  limestone  for  the  formation,,  and  in  1904 
l'lriclr  used  the  name  Spergen  in  exactly  the  same  manner.  Cumings' 
name  clearly  has  priority  as  a  formation  name,  and  by  the  application 
of  the  "law  of  priority"  his  name  must  be  adopted  and  is  consequently 
used  here. 

This  formation  is  represented  in  the  section  at  Warsaw,  Illinois,  by  a 
bed  of  limestone  about  8  feet  in  thickness.  It  increases  to  the  south, 
and  From  Jersey  to  Randolph  counties,  its  thickness  is  from  100  to  160 
feet.  The  formation  is  limestone,  almost  entirely  free  from  chert  through- 
out, although  the  beds  vary  greatly  in  lithologic  character.  Some  beds 
are  very  pure,  white  limestone,  in  many  places  containing  great  numbers 
of  bryozoans;  some  beds  are  oolitic,  while  others  are  decidedly  dolomitic. 
Many  years  ago  one  of  the  magnesian  beds  was  mined  in  Jersey  and  St. 
Clair  counties  for  the  manufacture  of  hydraulic  cement.  Towards  the 
summit  of  the  formation  some  of  the  beds  assume  lithologic  characters 
resembling  the  superjacent  St.  Louis  limestone,  the  transition  from  one 
formation  to  the  other  being  gradual,  without  a  distinct  stratigraphic 
break. 

The  fauna  of  the  Salem  limestone  has  long  been  known  as  the  Spergen 
Hill  fauna,  from  which  locality,  in  Indiana,  it  was  long  ago  described  by 
Hall  and  later  beautifully  illustrated  by  Whitfield.  The  fauna  contains  a 
large  number  of  species,  many  of  which  are  in  many  instances  diminutive 
in  form.  Brachiopods  and  fenestelloid  bryozoans  are  among  the  most 
conspicuous  members  of  the  fauna,  in  addition  to  which  many  gastropods 
and  pelecypods  are  locally  present,  besides  some  corals  and  other  forms. 

St.  Louis  limestone. — The  St.  Louis  formation  has  its  typical  develop- 
ment in  St.  Louis  and  in  the  Mississippi  river  bluffs  to  the  north  and  south 
of  that  city.  It  is  essentially  limestone  throughout,  in  some  places  quite 
free  from  chert,  and  in  others  with  conspicuous  chert  beds,  but  nowhere 
represented  by  such  extensive  chert  beds  as  are  commonly  present  in 
the  lower  portion  of  the  Osage  group.  The  limestones  of  the  formation 
are  more  or  less  heavy-bedded,  and  vary  considerably  in  lithologic  texture, 
but  are  rarely  oolitic.  A  very  characteristic  phase  is  exhibited  in  beds 
of  compact  bluish-gray  limestone,  very  brittle  and  breaking  with  a  conch- 
oidal  fracture,  and  generally  exhibiting  a  texture  almost  like  that  of 
lithographic  stone.     In  the  bluffs  north  of  Alton  the  formation  contains 

121st  Ann.  Rep.  Dept.  of  Geol.  and  Natl.  Resources,  Indiana,  pp.  291-427  (1897). 
2  Jour.  Geol.,  vol.  9,  p.  232  (1901). 

3U.  S.  Geol.  Survey,  Prof.  Paper,  No.  24,  p.  90  (1904);  Mo.  Bureau  Geol.  and 
Mines,  vol.  2,  2nd  ser.,  p.  110  (1904). 


GEOLOGICAL    INTRODUCTION  21 

some  important  dolomitic  beds  in  its  lower  portion,  but  such  beds  are 
much  less  conspicuous  further  south.  A  peculiar  topographic  feature 
marking  much  of  the  area  which  is  immediately  underlain  by  the  St. 
Louis  limestone,  is  the  remarkable  abundance  of  sink-holes ;  indeed  in 
some  portions  of  the  State  the  boundaries  of  the  formation  can  almost 
be  drawn  by  outlining  the  areas  of  sink-hole  topography. 

The  formation  has  a  thickness  of  from  30  to  40  feet  in  southeastern 
Iowa  ;  it  increases  in  thickness  to  the  south,  attaining  a  thickness  of  some 
250  feet  in  the  river  bluffs  above  Alton,  and  is  said  to  be  325  feet  thick 
in  the  St.  Louis  quadrangle.1  In  Monroe  and  Randolph  counties  the 
thickness  is  not  so  great  as  that  recorded  in  St.  Louis.  In  southeastern 
Iowa  the  formation  is  largely  a  brecciated  limestone,  and  in  the  bluffs 
above  Alton,  a  similar  brecciated  bed  about  20  feet  in  thickness  is  present 
near  the  middle  of  the  formation.  In  the  St.  Louis  quadrangle  brecciated 
beds  are  present  here  and  there  at  different  horizons  in  the  formation, 
but  further  south  this  feature  has  not  been  observed. 

The  fauna  of  the  St.  Louis  limestone  is  commonly  not  so  large  nor 
so  well  preserved  as  that  of  the  Salem  limestone,  and  in  many  places 
determinable  fossils  cannot  be  secured  through  considerable  thicknesses 
of  strata.  The  most  varied  faunas  have  usually  been  obtained  from  some 
of  the  cherty  beds.  A  species  of  the  bryozoan  genus  Cystodictya  is  one 
of  the  commonest  fossils  of  the  formation,  and  in  many  places  occurs  in 
great  numbers  upon  some  of  the  bedding  planes.  The.  corals  of  the  genus 
Lithostrotion,  L.  canadense  and  L.  proliferum,  are  good  index  fossils,  and 
where  they  occur  they  are  as  a  rule  present  in  abundance,  locally  almost 
entirely  constituting  beds  a  foot  or  more  in  thickness,  but  elsewhere, 
over  considerable  areas  and  through  considerable  thicknesses  of  strata, 
these  corals  may  not  be  found  at  all. 

IV.     STE.  GENEVIEVE  LIMESTONE 

Shumard2  first  differentiated  the  strata  immediately  above  the  St. 
Louis  limestone,  and  gave  to  them  a  distinct  formation  name,  the  Ste. 
Genevieve  limestone,  although  he  failed  to  point  out  that  the  two  forma- 
tions were  separated  by  a  distinct  line  of  unconformity.  This  uncon- 
formity has  been  seen  best  in  the  Mississippi  River  bluffs  below  Ste. 
Genevieve,  Missouri,  where  the  actual  contact  of  the  formation  upon  the 
subjacent  St.  Louis  limestone  may  be  observed  at  several  localities, 
showing  the  uneven  surface  of  the  lower  formation,  and  in  places  solution 
channels  along  joint  planes  which  have  been  filled  with  the  younger 
formation. 

lBull.  U.  S.  Geol.  Survey,  No.  438,  p.  23  (1911). 

2  Trans.  St.  Louis  Acad.  Sci.,  vol.  1,  p-  406  (1857);  Mo.  Geol.  Surv.,  Rept.  for 
1855-1871,  p.  293  (1873). 


22  MISSISSIPPIAN    BRACHIOPODA 

In  Illinois  the  Ste.  Genevieve  limestone  has  a  aotable  development  in 
the  valley  of  Fountain  Creek  and  its  tributaries  in  Monroe  County,  and 
extends  northward  as  Ear  as  Alton,  where  it  caps  the  Mississippi  River 

bluffs.     Worthen  included  all  of  these  beds  in  the  upper  portion  of  the 

St.   Louis  limestone. 

The  name  Ste.  Genevieve  has  been  revived  in  recent  years  by  Ulrich,1 
in  bis  study  of  the  Mississippian  section  in  western  Kentucky,  where  he 
lias  recognized  three  members  of  the  formation,  (lie  Kredonia  oolite,  the 
Rosidare  sandstone,  and  the  Ohara  limestone.  This  author's  criterion 
for  the  recognition  of  the  formation  seems  rather  to  be  a  lithologie  suc- 
cession, limestone  below  and  above  with  an  intermediate  sandstone,  than 
any  Eaunal  characteristics.  In  some  localities  the  beds  referred  by  him 
to  the  Ohara  carry  a  characteristically  Chester  fauna]  assemblage,  while 
at  other  points  the  Ohara  fauna  lacks  these  Chester  characteristics  and 
is  distinctly  older  in  general  complexion.  Because  of  this  uncertainty 
as  to  the  correctness  of  I'lrich's  interpretation  of  the  Ste.  Genevieve, 
his  subordinate  member  or  formation  names,  Fredonia,  Rosiclare  and 
Ohara  are  not  adopted  in  this  place,  although  in  certain  sections  in  Mon- 
roe County,  Illinois,  there  is  a  sandstone  stratum  with  limestone  both  above 
and  below  it  in  the  Ste.  Genevieve.  According  to  Ulrich  the  maximum 
thickness  of  his  Ste.  Genevieve  in  Kentucky  is  at  least  245  feet,  but  the 
greatest  measured  section  in  Monroe  County,  Illinois,  is  about  75  feet,  and 
it  probably  nowhere  exceeds  100  feet.  The  thickness  of  the  formation  in  its 
typical  localities  near  Ste.  Genevieve,  Missouri,  probably  does  not  exceed 
that  in  Monroe  County,  Illinois.  It  is  believed  by  the  writer  that  some 
room  for  doubt  exists  as  to  the  correctness  of  Ulrich 's  correlation  of  some 
of  the  beds  in  the  extreme  southern  counties  of  Illinois  which  have  been 
referred  to  the  Ste.  Geneveive  limestone  by  him,  and  the  description  of 
the  formation  herein  given  applies  only  to  its  typical  Mississippi  Valley 
expression. 

The  Ste.  Genevieve  includes  certain  remarkably  cross-bedded  lime- 
stones which  are  commonly  more  or  less  arenaceous;  some  of  the  most 
conspicuously  oolitic  limestones  in  our  entire  Mississippian  section;  and 
also  some  beds  which  are  wholly  arenaceous.  In  the  bluffs  at  Alton  about 
48  feet  of  limestone  and  more  or  less  arenaceous  strata  are  referable  to 
this  formation.  The  thickness  increases  to  the  south,  for  about  75  feet 
was  actually  observed  in  Monroe  County,  and  a  maximum  thickness  of 
100  feet  may  be  present.  In  Monroe  County,  where  the  formation  is  best 
known  by  the  writer,  the  basal  portion  comprises  the  remarkably  cross- 
bedded,  more  or  less  arenaceous  limestones  above  mentioned.  On  Andy's 
Creek,  in  this  county,  a  conspicuous  12-foot  sandstone  stratum  may  be 
seen  lying  about  20  feet  above  the  lowermost  observed  beds  of  Ste.  Gene- 

1U.  S.  Geol.  Survey,  Prof.  Paper,  No.  36,  p.  39  (1905). 


GEOLOGICAL   INTRODUCTION  23 

vieve  age  in  the  section,  and  below  about  20  feet  of  limestone.  This 
sandstone  is  very  fine-grained,  yellowish,  and  very  cross-bedded.  It  re- 
sembles, in  some  respects,  the  Rosiclare  sandstone  of  Hardin  County ; 
and  the  section  in  which  it  occurs  suggests  the  three-fold  division  of  the 
Ste.  Genevieve  of  that  county,  as  described  by  Ulrich.  In  Monroe  County, 
however,  this  bed  does  not  appear  to  be  a  continuous  formation,  but  only 
a  local  phase  of  the  formation  which  has  become  wholly  arenaceous. 

The  fauna  of  the  Ste.  Genevieve  limestone  is  in  part  a  recurrent 
fauna  from  the  Salem  limestone,  but  associated  with  these  recurrent 
forms  are  certain  others  which  are  characteristic  of  the  Ste.  Genevieve. 
The  best  index  fossil  of  the  formation  is  probably  Pugnoides  ottumwa, 
originally  described  from  the  Pella  beds  of  Iowa,  which  are  to  be  corre- 
lated with  these  Ste.  Genevieve  limestones.  Another  good  index  species, 
but  less  common  than  the  last,  is  Girtyella  indianensis,  which  is  also  typical 
of  the  Pella  beds  of  Iowa. 

V.     CHESTER  GROUP 

The  name  Chester  Group  was  originally  applied  by  Worth  en  to  those 
strata  of  the  Mississippian  series  typically  exposed  in  Randolph  County, 
from  the  base  of  the  so-called  "lower  sandstone  of  the  Chester  group" 
to  the  summit  of  the  Mississippian.  The  maximum  thickness  of  this 
series  of  beds  was  estimated  by  Worthen  to  be  at  least  600  feet.  A  careful 
measurement  of  the  Randolph  County  section  by  the  writer  gives  a  total 
thickness  of  about  550  feet,  although  a  thickness  of  743  feet  is  indicated 
in  the  Gilster  well  at  Chester. 

The  local  details  of  the  Chester  section  vary  from  place  to  place,  but  the 
larger  features  are  persistent  over  wide  areas.  The  lowermost  sandstone 
has  long  been  recognized  as  a  distinct  formational  unit  and  was  called 
Cypress  sandstone  by  Henry  Engelmann1  from  certain  extensive  ex- 
posures on  Cypress  Creek  in  Johnson  County.  The  series  of  beds  super- 
jacent to  the  Cypress  was  called  the  Kaskaskia  limestone  by  Hall.  More 
recent  field  investigations  have  made  it  clear  that  the  series  must  be 
subdivided,  and  Ulrich,  in  his  Kentucky  work,2  has  defined  two  forma- 
tions, the  lower  of  which  he  calls  Tribune  limestone  and  the  upper,  Birds- 
ville  formation,  which,  together,  constitute  the  Kaskaskia  of  Hall.  How- 
ever well  this  classification  may  apply  to  this  series  of  beds  in  Ken- 
tucky, it  is  inapplicable  in  the  typical  Illinois  section,  and  it  has  been 
found  necessary,  in  the  course  of  recent  field  work,  to  establish  an  entirely 
new  series  of  formational  units  for  the  Chester  group. 

l  Trans.  St.  Louis  Acad.  Sci.,  vol.  2,  pp.  189-190  (1863). 
2U.  S.  Geol.  Survey,  Prof.  Paper,  No.  36,  pp.  55-66  (1905). 


24  Mlssissil'i'lAN   BBACHIOPODA 

Brewerville  formation.  The  Lower  portion  of  the  Chester  group,  as 
recognized  by  Worthen,  and  by  Engelmann,  is  for  the  most  part  arenace- 
ous, and  the  name  Cypress  sandstone,  as  used  by  Engelmann,  and  later  by 
Ulrich,  wiis  originally  applied  to  this  lower  sandstone  member  of  the 
gioup.1  Recent  field  studies  have  brought  out  the  fact  that  two  distinct 
formations  arc  present  in  the  Cypress,  as  it  was  originally  defined,  sep- 
arated by  a  distinct  unconformity  and  overlap.  The  lower  of  these  two 
formations  is  the  Brewerville,  and  the  upper,  the  Renault  formation. 
The  Brewerville  sandstone  is  well-exposed  in  the  Mississippi  River  bluffs 
in  Brewerville  and  Prairie  du  Rocher  townships,  between  Modoc  and 
Prairie  du  Rocher,  in  Randolph  County,  where  the  thickness  of  the  for- 
mation is  about  80  feet. 

The  formation  consists  of  massive  beds  of  fine-grained  sandstone, 
which  as  a  rule  exhibit  much  cross-bedding.  In  its  unweathered  condition 
the  sandstone  is  a  light  yellowish-brown,  locally  nearly  white,  but  upon 
the  exposed  ledges  it  is  more  or  less  reddish-brown.  It  is  the  so-called 
"ferruginous  sandstone"  of  some  of  the  earlier  writers  upon  the  geology 
of  the  Mississippi  Valley. 

Wherever  the  Brewerville  has  been  critically  studied  by  the  writer,  it  is 
separated  from  the  subjacent  formations  by  a  distinct  erosion  uncon- 
formity, and  rests  locally  upon  the  Ste.  Genevieve  and  elsewhere  directly 
upon  the  St.  Louis  limestone.  In  much  of  this  area  a  conspicuous  basal 
breccia  is  present  at  the  contact  of  the  Brewerville  with  the  St.  Louis.  No 
fossils  have  ever  been  recorded  from  the  formation  and  none  have  ever 
been  found  by  the  writer. 

Renault  formation. — The  Renault  formation  has  its  typical  development 
in  the  valley  of  Horse  Creek  and  its  tributaries  in  the  eastern  portion 
of  Renault  Township  in  Monroe  County.  It  continues  northward,  where 
it  is  well  developed  east  and  northeast  of  Waterloo.  To  the  south  it  is 
exposed  in  the  Mississippi  River  bluffs  below  Modoc.  The  formation  is 
exceedingly  variable  in  its  lithologic  characters  and  includes  sandstone, 
shale,  and  limestone  members.  Some  of  the  sandstone  members  at  or  near 
the  top  of  the  Renault  closely  resemble  the  Brewerville,  but  they  are  com- 
monly thinner  bedded  and  are  associated  with  arenaceous  shales  and  with 
limestone  lenses  or  more  or  less  continuous  strata  of  limestone.  In  many 
localities  fossil  tree  trunks,  lepidodendroids,  are  present  in  the  sand- 
stones of  this  formation,  while  no  fossils  of  any  sort  have  been  observed 
in  the  Brewerville.  Northeast  of  Waterloo,  a  conspicuous  bed  of  varie- 
gated red  and  blue  or  gray  shale  is  a  notable  member  of  the  formation, 
and  other  less  important  beds  of  similar  variegated  shales  occur  elsewhere 

l  Engelmann  also  recognized  certain  beds  of  limestone  and  sandstone  in  Johnson 
County  which  he  believed  to  be  sub-Cypress  in  position,  but  no  sub-Cypress  Chester 
was  ever  recognized  by  Worthen  in  the  typical  Randolph  County  area. 


GEOLOGICAL    INTRODUCTION  25 

in  it.  The  thickness  of  the  Renault  varies  from  40  feet  or  less  to  a  maxi- 
mum of  100  feet  or  more. 

The  Renault  formation  commonly  overlaps  the  subjacent  Brewerville  to 
the  west  and  rests  directly  upon  the  St.  Louis  or  Ste.  G-enevieve  lime- 
stone in  unconformable  contact,  and  this  unconformity  is  also  present 
between  the  Renault  and  the  Brewerville  itself.  On  Hickman  Creek,  north- 
east of  Columbia,  the  Renault  rests  upon  the  Ste.  Genevieve  with  a  con- 
spicuous basal  conglomerate,  and  elsewhere  in  the  same  general  region  it 
rests  upon  the  Brewerville  with  a  basal  conglomerate,  mainly  of  limestone 
pebbles,  but  with  some  pebbles  of  crystalline  rock.  Eastward  from  the 
western  margin  of  the  Renault,  away  from  the  shore-line  of  the  period, 
the  limestone  members  of  the  formation  become  more  and  more  con- 
spicuous. 

In  some  of  the  limestones  and  associated  calcareous  shales  in  the 
Renault,  fossils  are  exceedingly  abundant,  the  facies  of  the  fauna  being 
typically  "Chester."  The  bryozoan  genus  Archimedes-,  however,  is  as 
a  rule  sparsely  represented  in  the  faunas  and  is  in  many  places  wholly 
absent,  although  in  at  least  one  locality  it  has  been  observed  in  abundance. 
The  genus  Lyropova,  on  the  other  hand,  is  in  many  localities  exceedingly 
abundant.  The  crinoid  fauna  of  these  beds  is  the  most  varied  and  best 
preserved  of  any  observed  in  the  Chester  group,  Talarocrinus  being  one 
of  the  commonest  genera  of  these  organisms. 

Yankeetown  formation. — Overlying  the  Renault  formation  is  a  thin  but 
most  persistent  siliceous  formation  of  peculiar  lithologic  character,  locally 
quartzitic.  Although  this  bed  is  entirely  unfossiliferous,  so  far  as  it  has 
been  observed,  it  has  served  as  a  key  formation  in  the  interpretation  of  the 
Chester  succession  to  a  greater  extent  than  any  other  formational  unit. 
Some  of  its  most  typical  exposures  may  be  seen  in  the  region  adjacent 
to  the  Yankeetown  school,  about  6  miles  southwest  of  Red  Bud,  from  which 
locality  the  name  of  the  formation  has  been  derived,  but  it  occurs  as  well 
in  the  extreme  north  of  the  area  of  the  outcrop  of  the  "Chester",  on 
Hickman  Creek,  northeast  of  Columbia,  and  near  Millstadt.  It  is  also 
well  exposed  in  the  Mississippi  River  bluff  section  one  and  one-half  miles 
below  Modoc,  and  at  many  intervening  localities. 

The  thickness  of  the  Yankeetown  is  probably  nowhere  over  20  feet, 
and  commonly  is  less.  Its  color  is  light,  commonly  gray  or  yellowish, 
or  in  many  localities  nearly  white.  It  is  very  irregularly,  and  more 
or  less  cross-bedded,  having  a  decidedly  knotty  appearance,  and  locally  is 
distinctly  banded.  It  is  commonly  more  or  less  arenaceous  and  in  some 
localities  certain  beds  are  quartzitic.  Where  the  formation  is  encountered 
in  wells  it  appears  to  be  a  very  hard,  siliceous  limestone,  and  in  dug  wells 
it  usually  puts  an  end  to  any  further  excavation.  The  Yankeetown  is  so 
hard  and  resistant  that  over  considerable  areas  the  superjacent,  beds  were 


L!ti  MISSISSIPPI^    BRACHIOPODA 

i 

removed  by  erosion  in  pre-Pennsylvanian  time,  and  in  such  areas  this 
formation  constitutes  the  floor  upon  which  the  Pennsylvanian  beds  have 
been  deposited. 

There  is  reason  to  believe  that  the  Yankeetown  rests  unconformably 
upon  the  subjacenl  Renault,  since  tbe  immediately  underlying  strata  are 
in  some  localities  Limestone,  in  others  sandstone,  and  in  still  others  shale. 

I', mil  Creek  formation  Above  the  Yankeetown  formation  is  a  series  of 
strata  approximating  60  feel  in  thickness,  which  are  shales  below,  passing 
into  limestones  above.  Near  the  base  of  this  Paint  Creek  formation, 
either  resting  directly  upon  the  Yankeetown  or  separated  from  it  by  a  few 
feet  of  blue  or  gray  shales  with  perhaps  some  thin  calcareous  beds,  is  a 
deep-red,  clay  member.  Its  summit  is  about  25  feet  above  the  top  of  the 
Yankeetown  chert  in  a  tributary  of  Paint  Creek  about  five  and  one-half 
miles  northeast  of  Prairie  du  Rocher,  from  which  locality  the  formation 
name  lias  been  taken.  In  fresh  exposures  this  red  bed  exhibits  little  or 
no  stratification  ;  on  being  subjected  to  atmospheric  agencies  it  first 
crumbles  into  small,  angular  fragments  which  eventually  disintegrate  into 
a  fine,  red  mud.  The  appearance  of  the  stratum  is  more  that  of  a  residual 
clay  than  anything  else  familiar  to  the  writer.  It  is  a  constant  member 
of  the  formation,  being  present  throughout  the  entire  extent  of  surface 
outcrop  of  this  portion  of  the  Chester  group,  and  being  recognized  in 
deep-well  records  beyond  this  region. 

No  fossils  have  been  found  in  the  red-clay  member  of  the  Paint  Creek 
formation,  but  in  the  succeeding  calcareous  shales  and  limestones  fossils 
are  common  in  many  localities.  Like  the  faunas  of  the  Renault,  the  Paint 
Creek  faunas  are  typically  Chester  in  facies  and  contain  many  of  the 
species  which  have  usually  been  reported  from  the  "Chester"  or  "Kas- 
kaskia"  limestone  in  the  past.  The  genus  Archimedes  is  more  commonly 
present  than  in  the  Renault,  although  it  is  as  a  rule  not  abundant,  as  is 
commonly  the  case  in  some  of  the  higher  beds.  Lyropora  is  also  a  com- 
mon form  in  some  localities,  and  among  the  brachiopods  Diaphragmus 
elegans  abounds  in  many  places. 

Runia  formation. —  Succeeding  the  upper  limestone  member  of  the  Paint 
Creek  is  a  shale  formation,  in  which  a  thin  sandy  member  is  usually  pres- 
ent near  or  a  little  above  the  middle.  These  beds  are  most  typically  ex- 
posed in  some  of  the  tributaries  of  Horse  Creek  northeast  of  Ruma,  and 
attain  a  thickness  of  25  to  40  feet.  The  shales  are  in  part  variegated  and 
in  part  blue  or  gray,  this  being,  in  fact,  the  highest  conspicuous  horizon 
of  variegated  shales  in  the  Chester  group.  The  shales  have  nowhere  been 
observed  to  be  fossiliferous,  but  in  the  sandstone  member  of  the  forma- 
tion, lepidodendroid  tree  trunks,  probably  identical  with  those  in  the 
Renault,  occur  in  many  localities. 


GEOLOGICAL   INTRODUCTION  27 

Okaw  formation. —  Succeeding  the  Ruma  formation  is  an  alternating 
series  of  limestones  and  shales  attaining  a  thickness  of  about  200  feet. 
The  shales  of  this  Okaw  formation  are  commonly  blue  or  gray,  rarely  with 
a  slight  admixture  of  red  and  blue,  which  is  such  a  conspicuous  feature  of 
some  of  the  shale  horizons  lower  in  the  section.  The  limestones  vary 
greatly  in  texture,  some  being  highly  crystalline,  some  oolitic,  and  others 
rarely  cherty.  Their  color  is  also  variable  from  gray  or  blue  to  nearly 
white.  At  least  four  conspicuous  limestone  horizons  are  present  in  the 
Okaw,  the  highest  of  which  is  the  quarry  ledge  at  Menard  in  the  South- 
ern Illinois  Penitentiary  prison  yard. 

Both  the  shales  and  the  limestones  of  the  Okaw  formation  are  com- 
monly fossiliferous,  and  in  many  localities  abundantly  so.  Within  the 
formation  are  several  more  or  less  distinct  faunal  zones,  although  the  de- 
tails of  the  faunal  distribution  of  the  fossils  has  not  yet  been  wholly 
worked  out.  At  the  base  of  the  lowermost  limestone  member  there  is 
commonly  present  a  zone,  several  feet  in  thickness,  which  is  especially 
marked  by  the  brachiopod  genus  Martinia,  this  being  the  only  horizon 
from  which  members  of  this  genus  have  been  recognized.  Associated 
with  Martinia,  in  most  localities,  are  great  numbers  of  bases  of  the  crinoid 
Agassizocrinus,  along  with  other  characteristic  Chester  forms.  A  few  feet 
higher,  still  in  the  basal  limestone  member  of  the  formation,  wing-like 
plates  from  the  ventral  disk  of  Pterotocrinus  depressus  occur  so  abund- 
antly in  many  localities  as  to  almost  entirely  cover  some  surfaces  of  the 
limestone,  in  fact  these  plates  of  several  species  of  Pterotocrinus  consti- 
tute a  very  notable  element  in  the  faunas  of  the  lower  members  of  the 
Okaw  formation.  Archimedes  is  especially  abundant  in  the  faunas  of  the 
lower  members  of  the  formation,  as  well  as  a  great  variety  of  other 
bryozoans. 

Some  60  feet  above  the  base  of  the  formation  occurs  a  \rery  constant 
oolitic  limestone  member,  10  or  more  feet  in  thickness,  with  a  fauna  in 
which  many  small  pelecypods  and  gastropods  are  present. 

The  summit  beds  of  the  formation  are  usually  calcareous  shales  with 
interbedded  thin  limestones,  and  locally  a  sandstone  ledge  10  to  12 
feet  in  thickness  is  present  a  few  feet  above  the  highest  heavy  ledge  of 
limestone.  These  shaly,  upper  Okaw,  beds  are  commonly  abundantly 
fossiliferous,  the  large  Mastoid,  Pentremites  sulcatus,  so  far  as  it  has  been 
observed  by  the  writer,  being  restricted  to  this  horizon.  Another  species 
which  has  been  found  in  most  localities  where  fossils  have  been  col- 
lected from  these  higher  beds,  and  which  has  been  seen  at  no  other 
horizon,  is  Archimedes  laxus. 

The  brachiopod  species  Camaroplioria  cxpla.nata  is  present  in  most  of  the 
Okaw  faunas,  and  has  been  observed  by  the  writer  only  rarely  in  any 
other  Chester  horizon.     This  formation  has  been  the  source  of  by  far  the 


28  iUlssissil'l'lAN    BRACHIOPODA 

greater  number  of  species  which  have  been  described  by  the  various 
writers  from  the  "Chester"  of  Illinois,  and  a  full  f aunal  list  of  the  forma- 
tion would  include  nearly  all  of  the  Chester  or  Kaskaskia  species  in  our 
literature. 

The  various  members  of  the  Okaw  formation  arc  well  exposed  in  the 
Mississippi  River  bluffs  above  and  below  the  tributary  Okaw  or  Kaskaskia 
valley,  this  valley  being  entirely  excavated  from  the  rocks  of  this  forma- 
tion at  its  point  of  juncture  with  the  valley  of  the  Mississippi,  hence  the 
name  here  adopted   for  the  formation. 

Menard  formation. — The  Menard  is  a  conspicuous  formation  of  lime- 
stone with  interbedded  shales,  well  exposed  in  the  middle  portion 
of  the  bluffs  at  Chester.  One  of  its  best  exposures  is  immediately  south- 
east of  the  hospital  for  criminal  insane  at  Menard.  In  its  typical  expres- 
sion, this  formation  is  a  thin  and  moderately  thick-bedded  limestone,  the 
bedding  planes  being  undulating  and  hummocky  in  character,  with  thin, 
shaly  partings.  In  places  these  shaly  partings  become  thicker,  and  shale 
beds  of  as  much  as  five  feet  or  more  in  thickness  are  present.  The  basal 
portion  of  the  formation,  where  it  is  exposed,  is  seen  to  be  shale,  as  much 
as  35  feet  of  fine,  blue,  clay  shale  being  present  in  some  localities  between 
the  top  of  the  Okaw  and  the  typical  limestone  beds  of  the  Menard.  The 
lithologic  character  of  the  limestone  of  •  the  formation  differentiates  the 
Menard  rather  sharply  from  most  of  the  limestone  strata  of  the 
Okaw.  The  limestones  of  the  lower  formation  are  commonly  more  or  less 
crystalline  or  granular,  often  crinoidal,  sometimes  oolitic,  and  usually 
free  from  chert.  In  the  Menard  the  limestones  are  nearly  always 
close-textured,  fine-grained  rocks,  and  there  may  be  a  small  amount  of 
chert;  they  are  brittle,  and  often  exhibit  a  conchoidal  fracture.  Because 
of  the  difference  in  texture,  the  weathered  surfaces  of  the  Menard  are 
commonly  smooth,  those  of  the  Okaw  usually  being  more  uneven.  The 
color  of  freshly  broken  surfaces  of  the  Menard  is  usually  a  bluish  gray, 
while  that  of  the  Okaw  limestone  is  commonly  lighter,  some  beds  being 
nearly  white.  Locally,  there  are  crystalline  strata  in  the  Menard  which 
closely  resemble  certain  of  the  Okaw  beds,  but  such  strata  are  always  of 
limited  thickness  and  usually  occur  in  the  higher  portion  of  the  forma- 
tion. The  thickness  of  the  Menard  is  about  80  feet.  It  is  well  exposed 
in  the  Mississippi  River  bluffs  from  Chester  to  Rockwood,  and  the  valley 
of  Mary's  River,  at  its  mouth,  is  excavated  entirely  through  this  forma- 
tion into  the  higher  beds  of  the  Okaw. 

The  fauna  of  the  Menard  is  very  different  from  that  of  the  Okaw. 
One  of  the  most  conspicuous  species  is  a  large  pelecypod  of  the  genus 
Sulcatopinna.  This  is  associated  with  several  other  species  of  pelecypods, 
and  with  the  large,  typical  forms  of  Composita  subquadraia  and  Spirifer  in- 
crebescens.    Pentremites  and  Archimedes  are  not  common  in  the  formation 


GEOLOGICAL    INTRODUCTION  29 

except  locally  in  some  of  the  uppermost  beds,  and  but  a  single  species  of 
Pentrcmites,  P.  cherokeeus  Hall,  has  been  collected. 

Palestine  formation.— The  formation  succeeding  the  Menard  is  arena- 
ceous throughout  in  most  sections,  consisting  in  part  of  heavy  beds 
of  sandstone  suitable  for  building  purposes,  and  in  part  of  thinly  bedded, 
ripple-marked  sandstones  or  arenaceous  shales.  Locally,  however,  more 
argillaceous  shales  are  well  developed  in  the  formation.  The  formation 
is  present  in  the  higher  portion  of  the  bluffs  at  Chester,  and  has  been 
quarried  at  several  points  for  building  stone.  The  buildings  of  the  peni- 
tentiary at  Menard  are  constructed  of  this  rock.  The  more  sandy  facies 
of  the  formation  are  exceedingly  well  exhibited  along  some  of  the  tribu- 
taries of  Tindall  Creek,  in  Palestine  Township  of  Randolph  County.  The 
thickness  of  the  formation  is  about  75  feet,  and  it  seems  to  lie  with  some 
degree  of  unconformity  upon  the  subjacent  Menard  limestone.  The 
only  fossils  which  have  been  seen  in  the  formation  are  fragments  of  Lepi- 
dodendron  trunks. 

Clore  formation.  —  The  highest  formation  in  the  Chester  Group  in 
Randolph  County,  is  a  limestone  immediately  overlying  the  Palestine 
sandstone.  The  greatest  thickness  actually  measured  is  30  feet,  but  it 
certainly  exceeds  this  thickness  in  many  localities.  The  transition  beds 
from  the  underlying  sandstone  to  the  Clore  limestone,  consist  of  arena- 
ceous and  calcareous  shales,  with  some  beds  of  limestone,  occupying,  in 
places,  an  interval  of  as  much  as  25  feet  below  the  more  continuous  lime- 
stone strata.  The  lithologic  characters  of  the  limestone  beds  are  vari- 
able, some  being  thin  bedded  and  almost  shaly,  others  being  similar  to  the 
Menard  in  texture  and  hardness,  but  usually  darker  in  color,  while 
others  are  more  granular  or  crystalline.  Some  shale  beds  are  included  in 
the  formation. 

The  Clore  limestone  caps  the  summits  of  the  hills  upon  which  the 
city  of  Chester  is  built,  and  it  outcrops  in  the  heads  of  several  of  the 
ravines  adjacent  to  the  town.  The  formation  also  caps  some  of  the 
liigher  hills  east  and  northeast  of  Chester  until  it  passes  beneath  the  over- 
lying Pennsylvanian.  Typical  exposures  of  it  occur  in  the  heads  of  the 
ravines  along  the  southwest  side  of  the  high  ridge,  extending  from  Clore 
school  to  the  Randolph  County  farm.  The  most  extensive  exposures 
which  have  come  under  observation  are  in  Bremen  Township  of  Randolph 
County,  about  two  miles  northeast  of  the  village  of  Bremen,  where  a  small 
anticlinal  flexure  causes  its  surface  outcrops  to  spread  out  on  either  side 
of  Little  Mary's  River. 

The  fossils  of  the  Clore  limestone  are  locally  more  conspicuous  than 
those  of  the  Menard.  Some  of  the  shaly  beds  are  filled  with  fossils 
and  are  suggestive  of  certain  phases  of  the  Okaw  formation,  but  the  asso- 
ciation of  species  is  different.  In  those  beds  resembling  the  Menard  in 
texture,  some  of  the  Menard  species  are  commonly  present. 


Descriptions  of  Genera 
and  Species 


Class  BRACHIOPODA 

Order  ATREMATA 

Family  LINGULIDiE 

Genus  LINGULA  Bruguiere 

Description. — Shell  thin,  linguiform  or  tongue-shaped,  subequivalvate. 
elongate-ovate  or  subquadrate  in  outline.  Brachial  valve  slightly  shorter 
than  the  pedicle  and  with  a  slightly  thickened  hinge-line.  The  pedicle 
opening  common  to  the  two  valves.  Surface  of  the  valves  usually  shining, 
smooth  or  marked  by  concentric  or  radiating  stria?.  Internally,  the 
muscular  impressions  are  numerous  but  usually  indistinct. 

Remarks.— The  genotype  of  IAngula  is  the  recent  species  L.  anatina,  but 
from  the  state  of  our  knowledge  of  the  characters  of  the  ancient  species 
which  have  been  referred  to  the  genus,  there  seems  to  be  reason  for  sepa- 
rating only  a  few  of  them  generically  from  the  living  forms.  It  is  true 
that  the  internal  characters,  especially  the  arrangement  of  the  muscular 
scars,  are  insufficiently  known  or  wholly  unknown  in  many  of  the  species 
which  have  been  described  from  Paleozoic  faunas,  and  it  is  possible  that 
with  future  increased  knowledge  of  these  characters  other  generic  dif- 
ferentiations may  be  drawn.  Ordinarily  it  is  difficult  or  impossible  to 
differentiate  between  the  two  valves  of  a  fossil  species  of  IAngula. 

LlNGULA  MEMBRANACEA  Winchell 

Plate  I,  Fig.  5 

1863.     Lingula  membranacea  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  3. 
1900.     Lingula  membranacea  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 
p.  65,  pi.  1,  fig.  20. 

Description.  —  Shell  ovate-subquadrangular  in  outline,  the  greatest  width 
towards  the  front,  the  valves  very  flat.  Postero-lateral  margins  nearly 
straight  as  they  approach  the  beak,  where  they  meet  in  a  very  broadly 
obtuse  angle,  rounding  into  the  lateral  margins  distally ;  lateral  margins 
nearly  straight  or  very  gently  convex,  diverging  slightly  anteriorly ;  the 
antero-lateral  margins  rounding  into  the  truncated  anterior  margin.  The 
beak  depressed  and  inconspicuous,  not  quite  reaching  the  posterior 
margin.     Surface  marked  only   by   concentric  lines  of  growth  varying 

—2 


34  MISSISSDPPIAN    BRACHIOPODA 

somewhat  in  strength  and  usually  situated  about  one-half  millimeter 
apart.  The  dimensions  of  the  type  specimen  are:  length,  12  mm. ;  great- 
est width,  8  nun. ;  width  at  postero-lateral  extremities,  (i  mm. 

Remarks.— The  holotype  only  of  this  species  has  been  observed,  an  illus- 
tration of  which  is  given  on  the  accompanying  plate.  The  specimen 
is  a  single  valve,  whether  pedicle  or  brachial  cannot  be  determined,  lying 
upon  a  fragment  of  fine-grained,  yellow  sandstone.  It  is  imperfect,  being 
somewhat  broken  upon  the  margins,  but  seems  to  be  sufficiently  distinct 
from  any  of  the  other  species  recognized,  and  may  be  distinguished  by  its 
ovate-subquadrangular  outline.  The  specimens  from  the  Waverly  for- 
mations of  Ohio  and  Pennsylvania  which  have  been  identified  with  this 
species  by  Winchell,  Meek,  and  Berrick,  are  all  specifically  different 
from  this  Iowa  shell. 

Horizon.     Chonopectus  sandstone  of  the  Kinderhook. 

Ijingula  i.ouisianensis  n.  sp. 
Pate  I,  Fig.  3 

Description.— Shell  small,  much  compressed,  ovate-subquadrangular  in 
outline,  the  lateral  margins  gently  convex  in  the  central  portion,  postero- 
lateral^ the  curvature  increases  and  passes  into  the  somewhat  narrowly 
rounded  posterior  margin,  antero-laterally  the  curvature  increases  more 
abruptly  than  posteriorly,  passing  into  the  broadly  rounded  or  sub- 
truncate  anterior  margin.  The  dimensions  of  a  nearly  complete  valve 
are:   length  9.7  mm.,  width  5.6  mm. 

Surface  of  the  brachial  ( ?)  valve,  in  the  internal  cast,  compressed  along 
the  postero-lateral  margins,  the  apex  of  the  convex  portion  of  the  valve 
lying  a  little  within  the  apex  of  the  posterior  margin,  a  slight  median 
ridge,  indicated  by  a  depression  in  the  surface  of  the  internal  impression, 
passes  anteriorly  from  near  the  apex  of  the  valve  for  nearly  half  its 
length. 

Surface  of  the  valve  nearly  smooth,  marked  by  fine,  but  somewhat 
irregular  lines  of  growth,  and  by  the  faintest  suggestion  of  radiating 
striae. 

Remarks.— The  specimen  from  which  the  above  description  has  been 
made  is  a  nearly  complete  internal  cast  of  what  seems  to  be  a  brachial 
valve,  with  only  fragments  of  the  shell  itself  preserved.  The  external  sur- 
face is  not  well  preserved  anywhere,  all  that  can  be  seen  being  restricted 
to  a  few  fragments  of  the  shell  still  retained  on  the  specimen.  In  size  and 
general  form  the  species  resembles  L.  gorbyi  from  the  Chouteau  lime- 
stone, from  which  species  it  may  be  distinguished  by  reason  of  its  sub- 
truncate  anterior  margin. 

Horizon.— Louisiana  limestone  of  the  Kinderhook. 


LINGULA  35 

Lingula  gorbyi  Miller 
Plate  I,  Figs.  1,  2 

1892.     Lingula  gorbyi  Miller,  Adv.  Sheets  18th  Rep.  Geol.  Surv.  lad.,  p  55. 

pi.  9,  figs.  3,  4. 
1894.     Lingula  gorbyi  Miller,  18th  Rep.  Geol.  Surv.  Ind.,  p.  309,  pi.  9, 

figs.  3-4. 

Description. — Shell  small,  subelliptical  in  outline,  the  width  more  than 
one-half  the  length.  The  dimensions  of  a  nearly  complete  valve  are: 
length  11  mm.,  width  7.2  mm. 

Valves  gently  convex,  the  anterior  margin  subsemicircular,  the  lateral 
margins  gently  convex,  the  postero-lateral  margins  nearly  straight  or 
gently  convex  and  meeting  at  the  beak  in  a  rounded,  obtuse  angle. 
Surface  marked  by  very  fine,  exceedingly  regular,  concentric  costa1,  from 
12  to  15  of  which  occupy  the  space  of  1  mm.,  and  usually  by  rather  ob- 
scure concentric  undulations. 

Remarks.— This  species  may  be  recognized  by  its  exceedingly  regular  con- 
centric costa\ 

Horizo n.— Chouteau  limestone  of  the  Kinderhook. 

Lingula  halli  White 

Plate  I,  Fig.  4 

1862.     Lingula  Halli  White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9,  p.  30. 

Description. — Shell  very  small,  longitudinally  subelliptical  in  outline, 
the  length  about  twice  the  width,  the  greatest  width  a  little  in  front 
of  the  middle ;  the  postero-lateral  margins  meeting  at  the  beak  in  an  acute 
angle,  the  lateral  margins  gently  convex,  the  anterior  margin  narrowly 
rounded.  The  dimensions  of  the  holotype  are :  length  6.1  mm.,  greatest 
width  2.8  mm.,  convexity  of  pedicle  valve  .8  mm. 

Pedicle  valve  rather  strongly  convex  in  proportion  to  the  width,  the 
greatest  convexity  posterior  to  the  middle ;  the  beak,  in  the  internal  cast, 
rather  abruptly  constricted  and  produced  posteriorly  a  little  beyond  the 
general  margin  of  the  valve.  Surface  marked  by  fine,  concentric  lines 
of  growth,  somewhat  variable  in  strength. 

Brachial  valve  imperfectly  preserved,  its  convexity  evidently  about 
equaling  that  of  the  pedicle  valve. 

Remarks.— The  holotype  of  this  species  is  an  internal  cast  of  what  is 
probably  the  pedicle  valve,  preserved  upon  a  fragment  of  white  chert. 
The  reverse  of  the  same  chert  fragment  preserves  small  portions  of  the 
shell  substance  of  this  valve  and  the  incomplete  brachial  valve,  somewhat 
displaced,  exhibiting  the  internal  surface  of  its  posterior  portion.  The 
species  differs  notably  from  any  of  the  other  recognized  Lingulas  in  the 
faunas  under  consideration,  in  its  narrowly  subelliptical  shell,  approach- 


36  Ailssissil'l'IAN    BRACHIOPODA 

in<i'  in  its  outline  L.  spalulata  of  the  Genesee  shale  of  the  New  York  Devon- 
ian.     The  species,  however,  is  larger  than  the  illustrated  examples  of  L. 
spatulata,  and  is  more  narrowly  rounded  at  the  anterior  margin. 
Horizon.     Burlington  limestone. 

LlNGULA  VARSOVI ENS1S    WortllC'll 

Plate  I,  Fig.  6 

1884.     Liiigula  varsoviensis  Worthen,    Hull.   No.   2,    111.   State  Mus.   Nat. 

Hist.,  p.  24. 
1890.    Lingula  varsoviemis  Worthen,  Geol.  Surv.  111.,  vol.  8,  p.  104,  pi. 

11,  fig.  8. 

Description.-  Shell  rather  large  for  the  genus,  subovate  in  outline,  the 
width  about  two-thirds  the  length,  the  greatest  width  anterior  to  the 
middle.  The  dimensions  of  the  holotype  are:  length  21.8  mm.,  greatest 
width  14  mm. 

The  valves  moderately  convex,  the  greatest  depth  posterior  to  the 
middle;  the  anterior  margin  subsemicircular,  the  lateral  margins  gently 
convex,  the  posterior  margin  shorter  than  the  anterior,  the  postero- 
lateral margins  meeting  at  the  beak  in  a  broadly  obtuse  angle  and  round- 
ing somewhat  abruptly  into  the  lateral  margins  distally,  the  beak  ap- 
parently not  prominent.  The  surface  marked  by  numerous,  regular, 
crowded,  concentric,  lines  of  growth  which  are  somewhat  variable  in 
strength,  becoming  more  crowded  towards  the  margins ;  the  median  one- 
fourth  of  the  valve  is  marked  by  faint,  radiating  costa?  which  are  only 
noticeable  anteriorly  from  the  middle  of  the  valve. 

h'emarks.— This  species  is  one  of  the  larger  members  of  the  genus  in 
the  faunas  under  consideration,  being  equalled  in  this  respect  only  by 
L.  indianensis.  These  two  species  are,  indeed,  closely  allied  and  should 
perhaps  be  considered  as  synonymous,  but  owing  to  the  limited  number 
of  specimens  examined,  the  holotypes  of  the  two  species,  it  is  not  possible 
to  certainly  determine  their  identity.  The  type  of  L.  indianensis  is  rela- 
tively a  little  broader,  a  character  which  may  be  due  to  the  somewhat 
crushed  condition  of  the  specimen,  the  concentric  markings  of  the  two 
specimens  are  entirely  similar  in  strength  and  expression,  but  the  L. 
indianensis  does  not  possess  the  faint  radiating  costse  in  the  median  portion 
of  the  valve  which  are  present  upon  L.  varsoviensis.  For  the  present  the 
two  species  will  be  considered  as  distinct,  their  separation  being  based  upon 
the  presence  of  the  faint,  radiating  costae  in  L.  varsoviensis  and  their  ab- 
sence in  L.  indianensis.  More  extensive  collections  may  show  that  this 
character  is  not  of  sufficient  value  to  be  used  as  a  means  of  separating 
the  two  forms  specifically,  in  which  case  Worthen 's  name  L.  varsoviensis 
will  be  applicable  to  all  of  the  specimens. 

Horizon.— Warsaw  beds. 


GLOSSINA  37 

Lingula  indianensis  Miller  and  Gurley 
Plate  I,  Fig.  7 

1894.     Lingula  indianensis  Miller  and  Gurley,  Bull.  No.  3,  111.  State  Mus. 
Nat.  Hist.,  p.  69,  pi.  7,  fig.  1. 

Description.— Shell  rather  large  for  the  genus,  subovate  in  outline,  the 
length  about  one-half  greater  than  the  width,  the  greatest  width  anterior 
to  the  middle.  The  dimensions  of  the  type  specimen  are :  length  21.8  mm., 
width  14.9  mm. 

Valves  gently  convex,  the  anterior  margin  subsemicircular,  the  lateral 
margins  gently  convex,  the  posterior  extremity  much  narower  than  the 
anterior,  the  postero-lateral  margins  meeting  at  the  beak  in  a  very  broadly 
obtuse  angle  and  rounding  rather  abuptly  into  the  lateral  margins ;  the 
beak  not  prominent.  Surface  marked  by  fine  concentric  lines  of  growth 
towards  the  beak,  which  become  coarser,  more  irregular  and  more  or  less 
undulatory  towards  the  margins. 

Remarks.— This  species  may  be  recognized  by  its  subovate  outline,  its 
rather  large  size,  and  its  more  or  less  irregular  concentric  markings.  It 
is  most  closely  allied  to  L.  varsoviensis,  from  which  it  can  be  distinguished 
only  by  the  absence  of  fine  radiating  costae  from  the  median  portion  of  the 
valve. 

Horizon.  —  Crawfordsville  shale. 

Genus  GLOSSINA  Phillips 

Description.  —  Shell  thin,  broadly  ovate-subtrigonal  in  outline,  acuminate 
posteriorly  and  rounded  anteriorly.  Surface  of  the  shell  visually  shining 
as  in  Lingula,  and  marked  by  concentric  lines  of  growth.  The  internal 
markings  of  the  valves  obscure  and  imperfectly  known. 

Remarks.— This  genus  has  been  established  to  include  a  few  linguloid 
species  which  differ  from  Lingula  proper  in  the  subtrigonal  outline  of  the 
shell.     The  internal  characters  of  the  shell  are  not  sufficiently  well  known, 
to  make  it  possible  to  determine  whether  or  not  the  arrangement  of  the 
muscular  scars  corresponds  with  that  of  Lingula. 

Glossina  sedaliensis  (Miller) 
Plate  I,  Fig.  11 

1892.     Lingula  sedaliensis  Miller,  Adv.  Sheets  18th  Rep.  Geol.  Surv.  Ind., 

p.  54,  pi.  9,  fig.  2. 
1894.     Lingula  sedaliensis  Miller,  18th  Rep.  Geol.  Surv.  Ind.,  p.  308,  pi.  9, 

fig.  2. 

Description. — Shell  triangularly  subovate  in  outline,  longer  than  wide, 
the  greatest  width  towards  the  anterior  margin.  The  approximate  di- 
mensions of  a  large  but  very  incomplete  example  are:  length  ±17  mm., 
width  ±13  mm. 


38  MISSISSIPPIAN   BRACHIOPODA 

Valves  depressed  convex,  the  anterior  margin  broadly  rounded,  ap- 
proaching subeircular,  passing  gradually  into  the  elongate,  nearly  straight 
postero-lateral  margins,  meeting  in  an  acute  angle  at  the  beak,  which 
is  sometimes  narrowly  rounded.  Surface  marked  by  slender,  raised, 
regular,  concentric  costa\  with  broad,  flattened  spaces  between,  about 
lour  or  five  occupying  the  space  of  one  millimeter  in  the  median  portion 
of  mature  shells  towards  the  front,  becoming  much  crowded  towards  the 
postero-lateral  margins. 

Remarks.  This  species  may  he  easily  recognized  by  its  subtriangular 
form  and  by  the  style  of  its  surface  markings. 

II union.     Chouteau  limestone. 

Glossi\\  uneolata  (Rowley) 
Plate  I,  Fig.  12 

1908.     Lingvla  linmlata  Rowley.  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 
ser.,  pp.  87  and  100,  pi.  19,  figs.  35-36 ;  pi.  20,  figs.  19-21. 

Description.—  Shell  small,  compressed,  broadly  triangularly  subovate  in 
outline,  the  greatest  width  anterior  to  the  middle.  Anterior  margin 
broadly  rounded  and  passing  regularly  into  the  lateral  margins,  the 
postero-lateral  margins  long,  gently  convex,  meeting  at  the  beak,  the 
angle  being  90  degrees  or  less.  The  dimensions  of  one  of  the  co-types  are : 
length  8  mm.,  width  7.5  mm. 

Ventral  (?)  valve  compressed,  the  greatest  depth  posterior  to  the  mid- 
dle, the  convex  curvature  of  the  surface  more  abrupt  to  the  postero- 
lateral margins.  Surface  marked  by  strong,  regular,  sublamellose,  con- 
centric markings. 

Remarks.— This  species  was  described  by  Rowley  from  two  specimens 
which  may  possibly  belong  to  two  different  species.  The  above  description 
is  based  upon  the  smaller  of  the  two  cotypes.  In  its  great  relative  width 
this  specimen  resembles  the  subtrigonal  linguloid  shells  which  have  been 
placed  in  the  genus  Glossina,  and  by  reason  of  that  character  alone  the 
species  is  here  included  in  that  genus.  The  species  differs  from  G. 
sedaliensis  of  the  Chouteau  limestone  in  its  smaller  size,  its  less  acute  beak, 
and  in  its  more  crowded  and  more  sublamellose  concentric  markings. 

Horizon. — Louisiana  limestone. 


OEBICULOIDEA  39 

Order  NEOTREMATA 

Family  DISCINID^ 

Genus  OEBICULOIDEA  d'Orbigny 

Description. — Shell  subcireular  or  subelliptical  in  outline,  inequivalvate. 
Pedicle  valve  nearly  flat  or  depressed-convex,  with  the  apex  excentric 
and  inclined  slightly  towards  the  posterior  margin ;  a  pedicle  groove 
originates  at  the  apex  of  the  valve,  passes  posteriorly  for  a  short  distance, 
beyond  which  point  it  is  continued  as  a  pedicle  tube  which  pierces  the 
substance  of  the  valve  very  obliquely,  opening  to  the  interior  near  the 
posterior  margin.  Brachial  valve  depressed  conical,  with  the  apex  ex- 
centric  and  inclined  posteriorly.  Surface  of  the  valves  smooth,  or  more 
commonly  marked  by  concentric  lines,  and  more  rarely  by  fine  radiating 
costae. 

Remarks.— The  species  of  this  genus  are  most  commonly  represented 
by  the  subconical  brachial  valves,  and  it  is  from  the  form,  proportions, 
and  surface  characters  of  these  valves  that  most  of  the  species  have  been 
differentiated.  Specimens  of  the  pedicle  valves  are  less  commonly  pre- 
served, and  when  seen  the  course  of  the  oblique  pedicle  opening  can  rarely 
be  traced. 

Orbiculoidea  capax   (White) 
Plate  I,  Fig.  13 

1862.     Discina  capax  White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9,  p.  30. 
1900.     Orbiculoidea  capax  Weller,   Trans.   St.  Louis  Acad.  Sci.,  vol.  10, 
p.  65,  pi.  1,  fig.  19. 

Description.— Shell  below  medium  size,  subcireular  in  outline,  length 
and  breadth  probably  about  equal.  The  dimensions  of  the  holotype  are : 
maximum  diameter  22  mm.,  convexity  of  brachial  valve  approximately 
5  mm. 

Pedicle  valve  not  known. 

Brachial  valve  depressed  conical,  the  apex  excentric  posteriorly  and 
inclined  towards  the  posterior  margin,  apparently  situated  about  one- 
fourth  or  one-fifth  the  length  of  the  valve  from  the  posterior  margin,  the 
greatest  convexity  of  the  valve  in  front  of  the  apex ;  the  surface  gently 
convex  from  the  apex  to  the  anterior  margin,  sloping  more  abruptly  to 
the  lateral  margins,  and  a  little  concave  to  the  posterior  margin.  The 
surface  marked  by  fine,  regular,  concentric  lines  of  growth,  and  by  more 
or  less  obscure  radiating  lines. 

Remarks.— The  holotype  of  this  species,  which  is  the  only  example  seen, 
is  a  much  crushed  and  imperfect  brachial  valve,  the  entire  outline  of 
which  cannot  be  determined.    The  central  portion  of  the  valve,  however, 


4.0  \i  ississil'IMAN    BRACHIOPODA 

is  well  preserved,  and  in  the  preparation  of  Ihc  above  dt'script ion  it  has 

been  assumed  thai  the  )'<> tin  and  cihiIoiiv  of  the  shell,  as  indicated  by  the 
growth   lines  of  Ibis  central   region,  represents  the  outline  of  the  entire 

shell.     The  species  lias  1 n   identified  by  Winched,  from  the  Marshall 

and   Waverly   formations  of  Michigan  and  Ohio,  but  the  specimens  so 

identified   are  probably   different    from    this  Chonopeetus  sandstone   shell. 

Horizon.    Chonopeetus  sandstone  of  ihe  Kinderhook. 

Orbiculoidka  sampsoni  (Miller) 
Plate  I,  Figs.  21,  22 

L891.     Discina  sampsoni   Miller.  Adv.  Sheets  17th  Rep.  Geol.  Surv.  Ind., 

p.  80,  pi.  13,  figs  10,  12. 
1892.     Discina  sampsoni  Miller,  17th  Rep.  Geol.  Surv.  Ind.,  p.  690,  pi.  13, 
figs.  10,  12. 

Description.— Shel]  small,  suboval  in  outline,  the  length  usually  greater 
than  the  width.  The  dimensions  of  one  of  the  type  specimens,  a  brachial 
valve,  are:    length  12.5  mm.,  width  12  mm.,  convexity  2.8  mm. 

Pedicle  valve  nearly  fiat,  marked  by  regular,  nearly  equidistant,  con- 
centric lines,  aboul  four  of  which  occupy  the  space  of  1  mm.;  the  pedicle 
opening  excentric. 

Brachial  valve  conical,  with  the  apex  excentric  posteriorly  and  in- 
clined posteriorly,  its  distance  from  the  posterior  margin  being  variable, 
the  greatest  depth  of  the  valve  usually  slightly  in  front  of  the  apex,  the 
surface  sloping  with  a  gently  convex  curvature  from  the  apex  to  the 
anterior  and  antero-lateral  margins,  becoming  slightly  concave  to  the 
postero-lateral  and  posterior  margins,  in  some  specimens  with  the  beak 
situated  more  than  usually  posterior,  the  posterior  slope  is  nearly  vertical. 
Surface  marked  by  fine,  regular,  concentric  lines  of  growth  which  are 
somewhat  variable  in  strength,  and  by  exceedingly  fine  radiating  lines 
wdiich  can  he  detected  upon  well-preserved  specimens  only,  with  a  good 
lens.  Internally,  a  slightly  elevated  and  very  narrow  ridge  extends 
anteriorly  from  the  apex  for  about  one-third  the  distance  to  the  anterior 
margin,  and  in  front  of  its  anterior  extremity  is  a  transverse  series  of  four, 
small,  slightly  elongated  papilla?. 

Remarks.— The  muscular  impressions  on  the  interior  of  the  brachial 
valve,  represented  by  the  slight  median  ridge  and  four  papillae  mentioned 
above,  have  been  observed  in  only  one  example,  one  of  the  co-types, 
where  they  appear  as  depressions  in  the  surface  of  the  internal  east 
where  the  test  has  been  removed. 

Horizon.— Chouteau  limestone  of  the  Kinderhook. 


ORBICULOIDEA  41 

Orbiculoidea  keokuk  (Gurley) 

Plate  I,  Figs.  14-17 

1884.     Distinct  Keokuk  Gurley,  New  Carboniferous  Foss.,  Bull.  No.  2,  p.  6. 

Description.  —  Shell  rather  large  for  the  genus,  subcireular  in  outline. 
The  dimensions  of  a  pedicle  valve,  one  of  the  eotypes,  are :  length  16.5 
ram.,  width  18  mm.      The  width  of  a  second  cotype  is  21  mm. 

Pedicle  valve  nearly  flat,  the  pedicle  opening  excentric,  its  external 
surface  marked  by  regular,  sublamellose,  concentric  lines  of  growth. 

Brachial  valve  depressed  conical,  the  apex  situated  at  about  one-fourth 
the  length  of  the  shell  from  the  anterior  margin,  the  surface  apparently 
gently  convex  from  the  apex  to  the  anterior  and  lateral  margins  and 
slightly  concave  to  the  posterior  margin.  The  surface  marked  by  fine, 
crowded,  rounded,  raised,  concentric  lines  of  growth  which  are  apparently 
somewhat  irregular  in  their  development  and  distribution.  Internally  a 
slight  median  ridge  extends  anteriorly  from  the  apex  for  about  one-third 
the  distance  to  the  anterior  margin  of  the  valve. 

Remarks.  —  The  above  description  is  based  upon  the  two  eotypes  of  the 
species  from  Crawfordsville,  Indiana.  The  brachial  valve  is  incomplete 
posteriorly  so  that  the  exact  position  of  its  apex,  relative  to  the  posterior 
margin,  cannot  be  determined.  The  length  of  the  valve  is  also  uncertain, 
and,  since  it  is  more  or  less  crushed,  the  depth,  as  well  as  the  contour  of 
the  sloping  surface  from  the  apex  to  margins,  cannot  be  accurately  deter- 
mined. The  shell  substance  is  largely  exfoliated,  but  enough  is  preserved 
to  show  the  character  of  the  surface  markings.  The  species  is  character- 
ized by  its  nearly  circular  outline  and  the  nature  of  its  surface  markings. 

Horizon.— Keokuk  ( Crawfordsville  shale) . 

Orbiculoidea  varsoviensis  (Worthen) 
Plate  I,  Figs.  23,  24 

1884.     Distinct  varsoviensis  Worthen,  Bull.  No.  2,  111.  State  Mus.  Nat.  Hist., 

p.  23. 
1890.     Discina  varsoviensis  Worthen,  Geol.  Surv.  111.,  vol.  8,  p.  102,  pi.  11, 

fig.  7. 

Description. — Shell  rather  large  for  the  genus,  subelliptical  in  outline. 
The  dimensions  of  the  holotype  are :  greater  diameter  19.5  mm.,  lesser 
diameter  16.1  mm. 

Pedicle  valve  nearly  flat;  the  pedicle  opening  situated  excentrically 
in  the  line  of  the  longer  axis  of  the  valve,  and  extending  from  the  center 
of  the  valve  half  way  to  its  posterior  margin,  its  lateral  margins  elevated 
upon  the  internal  surface  of  the  valve  to  form  an  elongate,  subovate 
prominence  which  is  probably  a  depression  or  excavation  externally. 
The  external  surface  marked  by  sublamellose,  concentric  lines  of  growth, 
from  two  to  three  of  which  occupy  the  space  of  1  mm. 


42  MISSISSIPPIAN   BRACHIOPODA 

Brachial  valve  imperfectly  preserved  in  the  only  example  observed, 
the  degree  of  convexity  not  known,  its  surface  marked  by  more  or  less 
regular,  sublamellose,  concentric  markings  similar  in  form  and  size  to 
those  of  the  opposite  valve,  and  by  very  faint  radiating  costae  upon  the 
flattened  spaces  between  the  concentric  markings. 

Remarks. — Only  two  specimens  of  this  species  have  been  examined 
l>\  t  he  writer,  these  being  the  original  types.  The  best  preserved  example 
is  the  inner  surface  of  a  pedicle  valve  which  has  been  illustrated  by 
Worthen.  The  second  specimen  is  a  fragment  of  limestone  upon  which 
two  valves  are  crushed,  partially  overlapping,  one  apparently  being  a 
pedicle  valve  and  Hie  other  a  brachial.  In  its  concentric  surface  markings 
the  species  resembles  0.  keokuk,  but  it  differs  from  that  species  in  its 
subelliptical  rather  than  subeircular  outline. 

Horizon. — Keokuk  limestone. 

Orbiculoidea  batesvillensis  Weller 
Plate  I,  Pigs.  19,  20 

1897.     Orbiculoidea  batesvillensis  Weller,  Trans.  N.  Y.  Acad.  Sci.,  vol.  16, 

p.  255,  pi.  18,  figs.  4-5. 
1909.     Liiigulidiscina  batesvillensis  Girty,  Bull.  U.  S.  Geol.  Survey  No.  377, 

p.  22,  pi.  1,  figs.  12-12a. 

Description.  —  Shell  subeircular  or  subovate  in  outline.  The  dimensions 
of  two  individuals,  the  cotypes,  are:  length  17  mm.  and  16  mm.,  width 
15.5  mm.  and  17  mm.,  convexity  3.8  mm.  and  3.5  mm. 

Pedicle  valve  not  known. 

Brachial  valve  depressed  convex,  subcorneal,  the  apex  small  and  in- 
conspicuous, inclined  posteriorly,  and  situated  excentrically  from  one- 
fifth  to  one-seventh  the  total  length  of  the  valve  from  the  anterior  margin, 
the  greatest  depth  of  the  valve  posterior  to  the  apex,  in  some  specimens 
notably  so ;  the  surface  gently  convex  throughout  from  the  central  portion 
to  the  margins,  except  for  a  short  space  back  of  the  apex.  The  surface 
markings  are  concentric  in  arrangement  so  far  as  can  be  determined 
from  the  internal  casts. 

Remarks.— This  species  was  established  upon  two  internal  casts  of  the 
brachial  valve  especially  characterized  by  their  small  apices  which 
are  distinctly  lower  than  the  greatest  convexity  of  the  valve  anteriorly. 
It  is  possible  that  the  apex  of  the  valve  would  be  somewhat  more 
prominent  in  specimens  preserving  the  shell  itself,  but  it  must  always 
have  been  inconspicuous  as  compared  with  other  species  of  the  genus. 

Horizon.— Batesville  sandstone,  Batesville,  Arkansas. 


CRANIA  43 

Family  CRANIID.E 
Genus  G  BAN  I A  Retzius 

Description. — Shell  subcircular  in  outline,  usually  more  or  less  unsym- 
metrical  in  its  growth,  inequivalvate.  Pedicle  valve  without  perforation 
for  the  passage  of  a  fleshy  pedicle,  attached  by  its  apex  or  by  its  entire 
external  surface  to  some  external  object.  Brachial  valve  depressed- 
subconical,  with  a  subcentral,  erect  or  posteriorly  directed  apex.  The 
interior  of  each  valve  is  marked  by  two  pairs  of  large  adductor  muscular 
scars,  the  posterior  pair  being  close  to  the  margin  and  widely  separated, 
the  anterior  pair  being  much  closer  together  and  subcentrally  located. 
The  external  surface  of  the  brachial  valve  marked  by  more  or  less  irregu- 
lar concentric  lines  of  growth,  by  regular  radiating  costas,  or  by  fine 
setae  or  pustules. 

Remarks. — The  more  regular  examples  of  the  brachial  valves  of  Crania 
may  be  distinguished  from  members  of  the  genus  Orbiculoidea  by  the 
more  nearly  central  position  of  the  apex  and  its  more  erect  position. 
These  valves  of  the  two  genera  also  may  be  commonly  differentiated  by 
reason  of  the  less  regular  manner  of  growth  in  the  genus  Crania. 

It  seems  hardly  justifiable  to  include  in  one  generic  group  all  the 
species  which  are  here  referred  to  the  genus  Crania.  Such  species  as 
Crania  roivleyi  having  the  shell  marked  by  conspicuous  radiating  costae 
can  hardly  be  congeneric  with  such  species  as  Crania  reposita,  for  in- 
stance, which  have  a  fundamentally  different  type  of  surface  markings, 
and  perhaps  the  species  marked  by  the  fine  setaa  or  pustules  should  be 
made  to  constitute  a  third  genus.  These  three  types  of  surface  markings 
persist  throughout  the  Paleozoic  faunas  where  these  shells  are  pres- 
ent, and  so  far  as  the  writer  is  aware,  there  is  never  any  question  as  to  the 
differentiation  of  the  groups.  No  generic  names  are  proposed  for  these 
distinct  groups  of  species  at  this  time,  however,  it  being  deemed  best  to 
defer  such  action  until  a  larger  number  of  species  from  all  the  different 
geological  time  periods  are  more  critically  studied. 

Crania  missouriensis  Weller 

Plate  I,  Pig.  30 

1909.     Crania  missouriensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  292, 
pi.  12,  fig.  1. 

Description.  —  Shell  rather  large  for  this  genus,  subcircular  in  outline. 
The  dimensions  of  the  type  specimen  are :   length  17  mm.,  width  17  mm. 

Pedicle  valve  attached  to  some  external  object,  in  the  case  of  the  type 
to  the  interior  of  the  shell  of  a  Productus,  its  characters  not  observed. 

Brachial  valve  depressed,  with  the  apex  rather  obscure  and  situated  ex- 
centrically  about  one-third  the  length  of  the  shell  from  the  anterior  mar- 


44  MISSISSIPPIAN    BRACHIOPODA 

gin;  iii  the  type  specimen  the  greatest  depth  of  the  valve  lies  posterior  to 
the  apex  near  the  center  and  the  central  portion  is  depressed  convex; 
towards  the  margin  the  sui  lace  becomes  concave,  but  lliis  contour  is 
doubtless  due  to  the  strongly  concave  surface  upon  which  this  individual 
has  grown,  and  in  other  situations  it  would  doubtless  be  depressed  convex 
throughout.  Surface  marked  by  rather  fine,  but  more  or  less  irregular 
and  uneven  concentric  markings. 

Remarks.— It  is  not  possible  to  compare  this  species  with  all  the  named 
forms  from  these  Mississippian  faunas  for  the  reason  that  several  have 
been  described  very  briefly  without  accompanying  figures.  It  seems  to  be 
sufficiently  distinct  from  all  of  them,  however. 

Horizon. — Fern  Glen  formation. 

Crania  dodgei  Rowley 

Plate  I,  Fig.  32 

1908.     Crania  >U><U\(J  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd  ser., 
p.  73,  pi.  17,  figs.  5-6. 

Description. — Shell  below  medium  size,  subcircular  in  outline,  the  holo- 
type  attached  to  a  shell  of  Spirifer  marionensis.  The  dimensions  of  the 
holotype  are:  greatest  diameter  17  mm.,  convexity  of  brachial  valve  6  mm. 

Pedicle  valve  entirely  covered  by  the  brachial  in  the  two  specimens  ex- 
amined, apparently  attached  by  its  entire  external  surface. 

Brachial  valve  depressed  conical,  the  apex  subcentral  or  somewhat  ec- 
centric in  position,  erect  or  slightly  inclined,  the  surface  sloping  in  all 
directions  from  the  apex  with  a  gently  convex  curvature.  The  surface 
marked  by  rather  strong,  crowded,  irregular,  concentric  lines  of  growth, 
and  by  very  fine,  obscure,  and  interrupted  radiating  stria'. 

Remarks. — Only  a  few  examples  of  this  species  have  been  observed  but 
their  irregular,  crowded,  concentric  lines  of  growth  with  obscure  radiat- 
ing striae  will  serve  to  distinguish  them  from  other  species. 

Horizon. — Louisiana  limestone. 

Crania  reposita  "White 
Plate  I,  Figs.  25,  26 
1862.     Crania  reposita  White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9,  p.  30. 

Description.— Shell  small,  subcircular,  subelliptical,  subovate  or  sub- 
quadrate  in  outline,  the  types  attached  to  a  shell  of  Spirifer  grimesi.  The 
dimensions  of  the  largest  of  the  type  specimens  are :  greater  diameter  13.5 
mm.,  lesser  diameter  11.1  mm. 

Pedicle  valve  firmly  cemented  by  its  entire  external  surface,  its  peri- 
phery thickened  in  a  ring-like  marginal  border ;  the  anterior  adductor 
muscular  scars  contiguous,  situated  a  little    eccentrically  and  distinctly 


CRANIA  45 

elevated  above  the  inner  surface  of  the  valve,  the  posterior  pair  situated 
just  within  the  raised  marginal  border  and  rather  widely  separated,  much 
less  elevated  than  the  anterior  pair. 

Brachial  valve  apparently  wanting  from  all  the  specimens  seen. 

Remarks. — This  species  is  known  only  from  the  types  which  consist  of 
five  individuals  attached  to  one  shed  of  Spirifer  grimesi.  The  species 
may  be  recognized  by  its  size,  the  raised  marginal  border  of  the  pedicle 
valve  and  the  conspicuously  raised  anterior  muscular  scars. 

Horizon.— Burlington  limestone. 

Crania  chesterensis  Miller  and  Gurley 

Plate  I,  Figs.  27-29 

1897.     Crania  chesterensis  Miller  and  Gurley,  Bull.  No.  12,  111.  State  Mus. 
Nat.  Hist.,  p.  47,  pi.  3,  figs.  24-26. 

Description.  —  Shell  small,  gregarious  in  habit,  subcircular  in  outline. 
The  dimensions  of  one  of  the  type  specimens  are:  greater  diameter  8  mm., 
lesser  diameter  7  mm. 

Pedicle  valve,  which  is  firmly  cemented  to  external  objects,  not 
observed. 

Brachial  valve  depressed,  thin  except  at  the  apex  and  about  the  outer 
margin,  the  apex  subcentral;  in  the  condition  of  preservation  of  all  the 
specimens  examined,  the  thinner  portion  of  the  valve  between  the  apex 
and  the  periphery,  appears  to  be  collapsed  or  depressed,  leaving  a  distinct- 
ly elevated  marginal  rim  and  a  node-like  subcentral  elevation  at  the  apex. 
Surface  marked  only  by  sublamellose,  concentric  lines  of  growth  which 
are  somewhat  crowded  near  the  periphery  but  are  much  less  conspicuous 
upon  the  collapsed  portion  of  the  valve  and  towards  the  apex. 

Remarks.  —  This  little  species  grows  most  commonly  upon  the  thickened 
borders  of  species  of  the  bryozoan  Lyropora,  but  it  also  occurs  sometimes 
upon  the  fenestrated  portion  of  the  same  bryozoan,  and  a  single  specimen 
has  been  observed  attached  to  the  shell  of  a  Spirifer.  The  species  can  be 
easily  recognized,  as  it  is  commonly  preserved,  by  the  raised  peripheral 
ring,  and  the  raised  central  node.  Whether  the  raised  peripheral  ring  is 
due  to  the  thickening  of  the  brachial  valve  at  the  margin,  as  has  been 
suggested  in  the  above  description,  or  whether  it  is  due  to  the  presence  of 
a  raised  or  thickened  margin  of  the  under  or  pedicle  valve,  cannot  be  cer- 
tainly determined  from  the  specimens,  but  perhaps  the  latter  supposition 
is  most  probable,  in  which  case  the  entire  brachial  valve  is  thin  except  at 
its  apex. 

Horizon.  —  Chester  group. 


-Hi  MISSISSIPPIAN    BRACHIOPODA 

Crania  rowleyi  Gurley 

Plate  I,  Figs.  37-39 

L883.     Grama  Eowleyi  Gurley,  Ne-w  Carb.  Foss.,  I-Jull.  No.  1,  p.  3. 

L892.     Crania  Eowleyi  Hall  and  Clarke,  Pal.  N.  V.,  vol.  8,  pt.  1,  pi.  4H,  fig. 

13. 
1908.     Crania  rowleyi  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd  ser., 

p.  73,  pi.  17,  figs.  3-4. 

Description.-  Shell  .small,  subcircular  or  subovate  in  outline,  attached 
to  shells  of  brachiopods  or  molluscs.  The  dimensions  of  a  normal  speci- 
men are:  maximum  diameter  10  mm.,  convexity  of  brachial  valve  2.5  ram. 

Pedicle  valve  not  observed,  firmly  attached  to  a  foreign  object. 

Brachial  valve  conical,  the  apex  of  the  cone  a  little  eccentric,  the  sides 
of  the  valve  from  the  apex  to  the  margin  nearly  straight  or  very  gently 
convex.  Surface  marked  by  fine,  abruptly  elevated,  radiating  costae, 
which  increase  regularly  by  intercalation,  and  about  three  of  which  oc- 
eupy  the  space  of  1  mm.  Crossing  the  costae  upon  shells  of  normal  size, 
there  are  usually  two  or  three  more  or  Less  conspicuous,  concentric  lines 
of  growth  occurring  at  nearly  regular  intervals. 

Remarks.—  This  little  shell  belongs  to  that  division  of  the  genus  Crania 
characterized  by  distinct  radiating  costae.  It  is  confined  to  the  Louisiana 
limestone  fauna,  so  far  as  known,  and  need  be  compared  only  with 
C.  blairi  of  the  Chouteau  limestone  which  has  sometimes  been  considered 
as  a  synonym.  C.  rowleyi,  however,  is  a  smaller  shell,  with  more  eccen- 
tric apex,  and  with  somewhat  coarser  costae. 

Horizon. — Louisiana  limestone. 

Crania  blairi  Miller 
Plate  I,  Figs.  34-36 

1892.     Crania  blairi  Miller,  Adv.  Sheets  18th  Rep.  Geol.  Surv.  Ind.,  p.  56, 

pi.  9,  figs.  5-6. 
1894.     Crania  blairi  Miller,  18th  Rep.  Geol.  Surv.  Ind.,  p.  310,  pi.  9,  figs. 

5-6. 

Description.— Shell  small,  subcircular  or  subovate  in  outline.  The  di- 
mensions of  a  normal  example  are :  maximum  diameter  14  mm.,  convexity 
of  brachial  valve  5  mm. 

Pedicle  valve  attached  to  foreign  objects  not  observed. 

Brachial  valve  conical  with  the  apex  of  the  cone  subeentral,  the  sides 
of  the  valve  from  the  apex  to  the  margins  gently  convex.  Surface  marked 
by  fine,  sharp,  radiating  costa?  which  increase  by  intercalation  and  which 
are  often  somewhat  flexuous,  especially  on  the  outer  half  of  the  valve, 
three  or  four  usually  occupying  the  space  of  1  mm.  Crossing  the  radiat- 
ing costae,  one  or  more  inconspicuous,  concentric  lines  of  growth  are  some- 
times present,  but  they  are  never  a  strongly  marked  feature. 


CRANIA  47 

Remarks. — This  species  has  sometimes  been  considered  as  a  synonym 
of  C.  rowleyi,  but  a  careful  comparison  of  numerous  examples  of  both 
species  has  led  to  the  conclusion  that  they  are  certainly  distinct.  C.  olairi 
attains  a  larger  size  than  C.  rowleyi,  which  alone,  of  course,  would  not  con- 
stitute a  good  specific  character ;  but  in  addition  the  apex  of  the  brachial 
valve  is  more  nearly  central  and  its  radiating  eostas  are  finer,  more  sharp- 
ly angular,  closer  together,  and  are  not  infrequently  somewhat  flexuose 
distally,  and  t lie  concentric  lines  of  growth  are  less  conspicuous. 

Horizon.  —  Chouteau  limestone. 

Crania  spiculata  Rowley 

Plate  I,  Fig.  31 

1908.     Crania  spiculata  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 
ser.,  p.  74,  pi.  17,  figs.  7-10. 

Description.  —  Shell  below  medium  size,  subcircular  in  outline,  the  holo- 
type  attached  to  a  shell  of  Syringothyris  hannibalensis.  The  dimensions 
of  the  holotype  are :  greatest  diameter  13.7  mm.,  convexity  of  brachial 
valve  5  mm. 

Pedicle  valve  apparently  cemented  by  its  entire  external  surface,  en- 
tirely covered  in  the  holotype  and  in  other  examples  observed. 

Brachial  valve  depressed  conical,  the  apex  central  and  erect,  the  sur- 
face sloping  in  all  directions  from  the  apex  in  straight  or  gently  convex 
lines.  The  surface  marked  by  more  or  less  obscure  concentric  lines  of 
growth  and  covered  by  fine,  closely  crowded  papilla?  wThich  are  slightly 
elongate  radially  with  their  distal  extremities  more  elevated  than  their 
proximal,  apparently  being  the  bases  of  fine,  appressed  spines  which  have 
covered  the  entire  surface  of  the  valve  in  life,  but  whose  length  cannot  be 
determined  from  the  fossil  specimens  studied. 

Remarks.— This  species  may  be  easily  recognized  by  its  finely  papillose 
surface  markings.  It  differs  from  the  similarly  marked  Burlington  lime- 
stone species,  C.  Icevis,  in  its  apparently  more  nearly  circular  outline,  its 
more  nearly  central  apex,  and  in  the  coarser  surface  papilhe. 

Horizon.— Louisiana  limestone. 

Crania  l^vis  Keyes 
Plate  I,  Fig.  33 

1894.     Crania  Icevis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  40. 

Description.— Shell  below  medium  size,  transversely  subelliptical  in  out- 
line, with  the  posterior  margin  truncated.  The  dimensions  of  one  of  the 
type  specimens  are :  greater  diameter  or  width  17  mm.,  lesser  diameter  or 
length  13  mm.,  length  of  posterior  truncated  margin  10.8  mm.,  convexity 
of  brachial  valve  4  mm. 

Pedicle  valve  not  known. 


1-8  MISSISSIPPIAN    BRACHIOPODA 

Brachial  valve  depressed  conical,  the  apex  situated  a  little  eccentric- 
ally towards  the  posterior  margin  and  inclined  posteriorly,  the  surface 
sloping  with  a  gently  convex  curvature  from  the  apex  to  the  lateral  and 
anterior  margins,  becoming  a  little  concave  to  the  posterior  margin.  In- 
ternally the  adductor  muscular  sears  are  well  defined,  the  anterior  pair 
rather  close  together,  situated  one  at  each  side  of  the  apex  of  the  valve, 
the  posterior  pair  somewhat  Larger  than  the  anterior,  marginal  in  position, 
much  farther  apart  than  the  posterior,  the  distance  from  center  to  center 
being  considerably  greater  than  their  distance  from  the  anterior  scars. 
External  surface  of  the  valve  marked  by  rather  obscure  concentric  lines 
of  growth,  and  entirely  covered  by  minute,  crowded  papillae  which  may 
indicate  the  presence  of  minute,  appressed  spines  upon  the  living  shell. 

Remarks.  The  name  Icevis,  uiven  to  this  species  by  Keyes,  suggests  a 
smooth  shell,  hul  the  specimen  here  described  and  illustrated,  which  was 
one  of  the  original  types,  is  (dearly  papillose  when  examined  under  a  lens, 
although  it  does  appear  almost  smooth  to  the  unaided  eye.  The  specimen 
is  a  silieitied  one,  and  it  is  possible  that  the  author  of  the  species  mistook 
these  minute  papilla1  for  irregularities  of  the  surface  due  to  the  silicifiea- 
tion  of  the  shell.  The  species  was  originally  recorded  from  the  Chouteau 
and  Burlington  limestones  at  Louisiana,  Mo.,  so  that  the  co-types  must 
have  been  at  least  two  in  number,  although  neither  of  them  were  illus- 
trated. The  specimen  here  figured  is  the  Burlington  limestone  specimen 
used  by  Keyes,  now  preserved  in  the  collection  of  Prof.  R.  R.  Rowley  at 
Louisiana.  No  other  example  has  been  observed.  The  species  differs 
from  C.  spicidata  of  the  Louisiana  limestone  in  its  less  circular  outline, 
the  more  eccentric  apex,  and  the  finer  surface  papillae. 

Horizon. — Burlington  limestone. 

Order  PROTREMATA 

Family  STROPHOMENID^ 

Genus  LEPT^NA  Dalman 

Description.  —  Shell  plano-convex  in  youth,  becoming  normally  con- 
cavo-convex at  maturity,  transversely  subtrapezoidal  or  semielliptical  in 
outline,  hinge-line  straight,  its  length  usually  the  greatest  width  of  the 
shell,  the  cardinal  extremities  often  subauriculate.  Pedicle  valve  with  a 
narrow  cardinal  area,  the  delthyrium  closed  by  a  convex  deltidium,  per- 
forated at  the  apex  of  the  beak  by  a  foramen  which  is  commonly  filled  at 
maturity.  Brachial  valve  with  a  cardinal  area  narrower  than  that  of  the 
pedicle  valve,  the  cardinal  process  large  and  bifid,  surrounded  posteriorly 
by  a  well-developed  chilidium.  The  surface  of  both  valves  marked  pos- 
teriorly by  conspicuous  concentric  corrugations  and  where  these  cease 


LEPTVENA  49 

the  valves  are  more  or  less  abruptly  and  often  rectangularly  deflected  to 
form  a  conspicuous  anterior  slope.  The  entire  external  surface  is  also 
covered  by  fine,  regular,  radiating  costse  which  increase  by  intercalation 
and  bifurcation,  and  by  still  finer  concentric  markings. 

Remarks. — Wherever  members  of  this  genus  have  been  recorded  they 
have  usually  been  referred  to  the  single  species  L.  rhomboidalis  Wilck.,  aud 
while  it  is  true  that  representatives  of  this  so-called  species  throughout  its 
entire  geologic  range,  resemble  each  other  more  or  less  closely,  it  is  also 
true  that  the  individuals  associated  together  in  any  one  fauna  do  pos- 
sess characteristics  by  means  of  which  they  may  lie  distinguished  from 
any  other  group  of  individuals  from  another  fauna.  There  may  be  a 
difference  of  opinion  as  to  whether  these  groups  should  be  given  specific 
or  varietal  rank,  hut  in  the  opinion  of  the  writer  they  should  be  consid- 
ered as  distinct  species,  there  being  no  advantage  in  using  varietal  names 
for  groups  of  individuals  which  can  be  clearly  differentiated,  and  for  the 
purposes  of  the  stratigrapher  it  is  necessary  that  the  several  forms  should 
have  some  designation  by  which  they  may  be  referred  to.  Among  the 
Mississippian  faunas  here  considered,  there  are  at  least  two  forms  which 
are  sufficiently  distinct  to  be  easily  differentiated,  neither  one  of  which, 
it  is  believed,  can  be  referred  to  the  typical  L.  rhomboidalis.  In  Great 
Britain  the  Mississippian  form  of  Leptmna  is  commonly  called  L.  analoga, 
and  one  of  the  forms  in  our  faunas  is  here  referred  to  that  species,  al- 
though it  is  not  possible  to  determine  from  Phillip's  original  description 
and  figure  just  what  the  essential  characters  of  the  species  are. 

Lept^na  analoga   (Phillips) 

Plate  II,  Figs.  1-10 

1836.     Producta   analoga  Phillips,   Geol.   Yorkshire,   vol.  2,   p.  215,   pi.   7, 

fig.  10. 
1839.     Strophomcna    rhomboidalis    var.    analoga    Davidson,    Brit.    Foss. 

Brach.,  vol.  2,  p.  119,  pi.  28,  figs.  1-2. 
1874.     Strophomenn  rhomboidalis  White,  Prelim.  Rep.  Inv.  Foss.,  p.  17. 
1877.     Strophomcna  rhomboidalis  White,  U.  S.  Geog.  Surveys,  W.  100th 

Mer.,  vol.  4,  p.  85,  pi.  5,  fig.  5. 
1877.     Stropliomcna  rhomboidalis  Hall  and  Whitfield,  U.  S.   Geol.  Expl., 
40th  Par.,  vol.  4,  p.  253,  pi.  4,  fig.  4. 

1888.  Strophomena  rhomboidalis  Herrick,  Bull.  Sci.  Lab.  Denison  Univ., 

vol.  4,  pi.  9,  fig.  6. 

1889.  Strophomcna  rhomboidalis  Herrick,  Am.  Geol.,  vol.  3,  pi.  4,  fig.  6. 
1892.     Leptama  rhomboidalis  Hall    and    Clarke,  Int.  to  Study  of  Brach., 

pt.  1,  pi.  13,  fig.  9. 
1892.     Leptama  rhomboidalis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  8,  figs.  30-31;  pi.  20,  fig.  24. 
1894.     Plectambonites  rhomboidalis  Keves,  Mo.  Geol.  Surv.,  vol.  5,  p.  70, 

pi.  39,  fig.  6. 


50  \i  ississil-l'IAN   BRACHIOPODA 

1895.    Strophomena  rhomboidaUs  Herrick,  Geol.  Surv.  Ohio,  vol.  7,  pi.  20, 

fig.  6. 
1899.     Leptcena  rhomboickMs  Girty,  Mon.  U.  S.  Gool.  Survey,  vol.  32,  p.  525. 
L904.     Lepta  na  rhomboidalis  Girty,  Prof.  Paper  U.  S.  Geol.  Survey,  No.  21, 

p.  48,  pi.  10,  fig.  3. 
1909.      LcpUiriKi  rhomboidulis  WYllor,  Hull.  Gool.  Soc.  Am.,  vol.  20,  p.  292, 
pi.  12,  figs.  2-3. 

Description. — Shell  of  medium  size  or  larger,  subtrapezoidal  in  outline, 
wider  than  long,  the  greatest  width  along  the  hinge-line,  the  cardinal  ex- 
tremities angular,  sometimes  rather  broadly  auricular.  The  dimensions 
of  a  nearly  complete  example  are:  length  25  mm.,  width  along  hinge-line 
es1  imated  40  mm. 

Pedicle  valve  depressed  convex  in  the  uinhonal  region,  flattened  ante- 
riorly and  laterally  to  near  the  margin  of  the  valve  where  it  is  abruptly 
geniculate,  the  deflected  portion  variable  in  width  with  age,  sometimes 
having  a  width  equal  to  more  than  one  hall'  the  length  of  the  flattened 
portion  of  the  valve.  The  surface  of  the  valve  at  the  geniculate  margin  is 
sometimes  raised  in  an  elevated  border  which  is  highest  in  the  median 
portion  of  the  valve  in  front,  becoming  gradually  reduced  along  the 
lateral  margins  anteriorly  and  becoming  obsolete  towards  the  cardinal 
extremities ;  the  deflected  border  of  the  valve  is  sometimes  sinuate  in  front, 
the  sinus  when  present  is  broad,  ill-defined,  and  shallow,  and  does  not 
continue  across  the  flattened  portion  of  the  valve ;  beak  small,  slightly  or 
not  at  all  extended  beyond  the  cardinal  margin,  and  not  incurved,  usually 
pierced  by  a  minute,  subcircular  foramen  which  often  becomes  filled  in 
mature  shells ;  cardinal  area  narrow,  flat  or  slightly  concave,  sloping  pos- 
teriorly from  the  hinge-line  and  lying  at  an  angle  of  45  degrees  or  less  to 
the  plane  of  the  valve,  the  lateral  margins  sharply  defined ;  delthyrium 
broadly  triangular,  closed  at  its  apex  by  a  small  deltidium,  the  greater 
portion  of  it  filled  by  the  cardinal  process  of  the  opposite  valve.  Intern- 
ally the  cardinal  teeth  are  rather  thick  and  short ;  near  or  a  little  poste- 
rior to  the  middle  of  the  lateral  margins,  a  rather  narrowly  elevated  ridge 
passes  posteriorly  with  a  gentle  curvature  towards  the  middle  of  the 
hinge-line,  the  narrowly  triangular  areas  toward  the  cardinal  extremities, 
which  are  isolated  by  these  ridges,  are  rather  deeply  excavated.  The  mus- 
cular scar  is  deeply  concave,  broader  than  long,  subrhomboidal  to  sub- 
elliptical  in  outline,  and  is  surrounded  laterally  and  anteriorly  by  an 
angular  ridge  which  terminates  on  either  side  just  in  front  of  the  cardinal 
teeth;  the  length  of  the  scar  is  one-third  or  less  than  one-third  the  total 
length  of  the  valve,  it  is  divided  along  its  median  line  by  a  low  angular 
ridge  originating  just  within  the  anterior  border  and  becoming  obsolete 
towards  the  posterior  border,  on  each  side  of  this  ridge  are  the  narrow 
and  elongate  adductor  scars,  beyond  which  the  much  larger  diductor  scars 
occupy  the  greater  portion  of  the  total  area;  the  primary  trunk  of  the 


LEPT^NA  51 

vascular  impressions  originates  at  the  anterior  border  of  the  muscular 
scar  in  the  middle  of  the  valve,  it  passes  towards  the  anterior  margin  a 
short  distance  and  divides  into  two  lateral  limbs  which  have  a  direction 
subparallel  with  the  anterior  and  lateral  margins  of  the  valve,  each  lateral 
I i ml i  giving  oft'  branches  at  nearly  right  angles  towards  the  margin  of  the 
valve,  each  branch  divides  into  two  or  three  before  reaching  the  margin, 
and  those  in  the  anterior  portion  of  the  valve  often  anastomosing;  between 
the  two  lateral  limbs  of  the  vascular  markings  and  the  muscular  scars 
the  inner  surface  of  the  valve  is  thickly  papillose,  with  a  few  similar,  but 
more  scattered  papilla*  within  the  vascularly  marked  area. 

Brachial  valve  slightly  concave  near  the  beak,  becoming  flattened  or 
slightly  convex  to  the  line  of  geniculation  of  the  pedicle  valve,  at  which 
line  the  valve  is  abruptly  deflected  to  conform  with  that  valve ;  mesial 
fold  entirely  obsolete  or  represented  by  a  slight,  broad,  low,  ill-defined, 
longitudinal  elevation  across  the  deflected  border  of  the  valve;  cardinal 
area  narrower  than  that  of  the  opposite  valve  and  meeting  it  along  the 
hinge-line  in  an  angle  of  45  degrees  or  less,  the  posterior  extremity  of  the 
cardinal  process  protuberant  at  the  middle  of  the  cardinal  area  and  sur- 
rounded by  the  chilidium.  Internally  a  conspicuous,  elevated,  angular 
ridge  follows  the  external  line  of  deflection  of  the  valve  except  near  the 
cardinal  margin,  where  its  terminal  portions  curve  towards  the  center  of 
the  valve;  the  ridge  increases  in  prominence  with  age,  and  gives  to  that 
subelliptical  portion  of  the  valve  bounded  by  it,  a  deeply  concave  contour ; 
the  external  surface  of  the  ridge  slopes  steeply  to  the  margin  of  the  valve 
except  towards  the  cardinal  extremities  where  it  is  deflected  laterally ; 
the  cardinal  process  bifid;  the  muscular  scars  occupy  a  subrhomboidal 
area  bordered  by  an  elevated  ridge  and  are  divided  by  a  median  ridge ; 
the  vascular  markings  have  an  arrangement  similar  to  those  of  the  oppo- 
site valve ;  the  surface  sloping  from  the  marginal  ridge  to  the  outer  mar- 
gin of  the  valve  is  marked  by  rather  coarse,  elongate  papillae  irregularly 
arranged  in  radiating  lines. 

The  surface  markings  of  both  valves  consist  of  a  series  of  conspicuous, 
concentric  corrugations  covering  the  flattened  portions  of  the  valves ; 
these  corrugations  are  variable  in  size  upon  the  same  individual,  growing 
successively  coarser  from  the  beak  to  the  margin,  and  also  vary  among 
different  individuals,  the  minimum  width  being  less  than  1  mm.  and  the 
maximum  2  mm.  or  more ;  these  wrinkles  are  often  more  or  less  discontin- 
uous and  sometimes  divide  or  anastomose,  and  towards  the  cardinal  ex- 
tremities their  direction  is  usually  gradually  deflected  laterally ;  crossing 
the  concentric  wrinkles  and  continuing  to  the  shell  margin,  are  a  series  of 
fine,  rounded,  radiating  costte  which  increase  by  bifurcation  and  intercal- 
ation, about  three  or  four  of  these  usually  occupying  the  space  of  one 
millimeter;  the  entire  surface  also  marked  by  exceedingly  fine  concentric 
lines  of  growth. 


ILLINOIS  STATE 

6E0LOGICAL  SURVEY 

LIBRARY 


52  m  ississii'l'i  w    BBACHIOPODA 

Remarks.-  The  shells  here  included  in  Phillip's  species  L.  analoga  have 
almost  always  been  referred  to  the  supposed  long-lived  species  L.  rhom- 
boidalis.  As  set  forth  in  the  foregoing  discussion  of  the  genus  Leptcena, 
it  seems  best  to  spilt  up  this  so-culled  species  into  several  groups  of  indi- 
viduals which  can  conveniently  be  considered  as  distinct  species.  In  our 
Mississippiau  faunas  two  such  forms  are  recognized,  of  which  the  one  here 
described  is  the  more  common.  It  is  referred  to  Phillip's  species  because 
of  its  apparent  identity  with  that  species  as  illustrated  by  Davidson,1  the 
original  definition  and  figure  of  Phillips  being  too  imperfect  to  allow  of 
certain  identification.  The  different  individuals  of  the  species  exhibit 
some  variation  in  the  coarseness  of  the  concentric  corrugations  of  the 
shell  and  in  the  relative  width  of  the  anterior  subtruncate  margin  and 
the  consequent  amount  of  divergence  of  the  lateral  margins  of  the  shell, 
the  finer  corrugations  and  the  more  divergenl  lateral  margins  usually 
being  associated. 

Horizon. — Kinderhook  and  Lower  Burlington. 

Lept^:na  convexa  n.  sp. 

Plate  U,  Pigs.  11-16 

1901.     Leptcena  rhomb oidalis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
pp.  159  and  180,  pi.   14.  figs.  19-20,  and  pi.  16,  figs.  7-8. 

Description. — Shell  of  medium  size  or  somewhat  larger,  subsemicircular 
in  outline,  wider  than  long,  the  greatest  width  at  or  near  the  hinge-line, 
the  cardinal  extremities  usually  nearly  rectangular.  The  dimensions  of  a 
nearly  complete  pedicle  valve  are :  length  21  mm.,  greatest  width  28  mm., 
convexity  8  mm. 

Pedicle  valve  depressed  convex  in  the  umbonal  region,  this  convexity 
continuing  for  two-thirds  or  more  of  the  length  of  the  shell,  beyond 
which  it  curves  more  abruptly  to  the  anterior  and  lateral  margins,  the 
surface  somewhat  compressed  towards  the  cardinal  extremities,  mesial 
sinus  wanting;  beak  small,  scarcely  produced  beyond  the  cardinal  margin 
and  not  incurved,  perforated  at  its  apex  by  a  small,  circular  foramen 
which  sometimes  becomes  filled  in  mature  shells;  cardinal  area  narrow. 
Internal  characters  of  the  valve  not  observed. 

Brachial  valve  gently  concave  posteriorly,  becoming  more  strongly 
curved  towards  the  lateral  and  anterior  margins  with  no  suggestion  of 
a  mesial  fold  or  sinus,  somewhat  flattened  towards  the  cardinal  extrem- 
ities.    Internal  characters  of  the  valve  not  observed. 

The  surface  markings  of  both  valves  consist  of  concentric  corrugations 
which  cover  the  more  gently  curved  posterior  portion,  these  corrugations 
being  either  quite  regular  in  their  development   or  exhibiting   a   con- 

iMon.  Brit.  Carb.  Brach.,  p.  119,  pi.  28,  figs.  1-13   (1860). 


SUHUCHERTELLA  53 

siderable  amount  of  irregularity;  they  are  narrower  and  less  deeply 
impressed  towards  the  beak,  becoming  regularly  stronger  distally ;  fine 
radiating  costse  cross  the  concentric  corrugations  and  continue  to  the 
shell  margin,  from  three  to  five  occupying  the  space  of  one  millimeter, 
and  these  costa;  are  again  crossed  by  still  finer  concentric  markings. 

Remarks.— This  species  differs  from  L.  analoga  in  the  absence  of  the 
distinctly  flattened  posterior  region  which  passes  into  the  anterior  and 
anterolateral  border  by  an  abrupt  geniculate  deflection  of  the  valves ; 
instead  of  this  the  valves  are  more  regularly  curved  throughout,  the  sur- 
face curving  somewhat  more  rapidly  towards  the  margin  instead  of 
being  abruptly  deflected.  Upon  this  species  the  fine  radiating  costa?  are 
also  more  strongly  and  more  regularly  developed,  although  no  broader; 
the  concentric  corrugations  are  less  deeply  impressed  and  a  little  less 
regular  in  their  development,  and  the  fine  concentric  markings  are  more 
conspicuous.  In  their  occurrence  the  two  species  are  not  associated 
together  in  the  same  fauna,  and  the  present  species  is  less  commonly 
seen  than  is  L.  analoga. 

Horizon. — Kinderhook. 

Genus  SCHUCHERTELLA  Girty 

Description.— Shell  biconvex,  hinge-line  usually  equaling  or  sometimes 
a  little  shorter  than  the  greatest  width,  the  lateral  and  anterior  margins 
rounded.  Pedicle  valve  with  a  moderately  high  cardinal  area,  with  a 
large  delthyrium  which  is  closed  to  the  apex  by  the  deltidium.  The 
cardinal  area  is  differentiated  into  two  regions,  the  outer  or  primary  area 
and  the  inner  or  secondary  area  slightly  raised  above  the  former,  the 
lines  separating  the  two  regions  pass  from  the  apex  of  the  beak  to  points 
about  midway  between  the  delthyrium  and  the  cardinal  extremities  upon 
the  hinge-line;  the  entire  area  is  marked  by  horizontal  lines  of  growth  in 
addition  to  which  the  secondary  area  is  marked  by  vertical  strias  which 
become  more  noticeable  with  the  wearing  of  the  surface.  Internally  the 
dental  lamella1  are  reduced  to  mere  thickenings  of  the  inner  surface  of 
the  cardinal  area  at  the  margins  of  the  delthyrium;  a  median  septum  is 
absent.  The  brachial  valve  is  a  little  less  convex  than  the  pedicle  valve, 
with  a  narrow  cardinal  area,  and  a  short  cardinal  process. 

Remarks.— The  genus  Schuchericlla,  as  originally  proposed  by  Girty 
for  those  non-septate  orthotetoid  shells  which  Hall  and  Clarke  referred 
to  Orthothetcs,  includes  two  distinct  generic  types,  as  has  been  pointed 
out  by  Thomas.1  The  first  of  these,  ScJmchertella  proper,  as  typified  by 
'the  genotype  S.  lens,  includes  the  lesser  number  of  the  Mississippian 
species,  the  second  and  larger  group  of  species  being  designated  by  the 

lMem.  Geol.  Surv.  Gt.  Brit,  Paleontology,  vol.  1,  pt.  2,  p.  92   (1910). 


54  MISSISSIPPI^    BRACHIOPODA 

generic  name  Schellmenella.  The  most  essential  characters  of  Schuchert- 
iila  are  the  biconvex  .shell  and  the  undeveloped  dental  plates.  The  last 
of  these  characters  cannol  always  be  detected  in  the  specimens  studied, 
but  so  far  as  has  been  observed  these  two  characters  are  always  asso- 
ciated. 

ScilUCJIEKTELLA   FERNGLENENSIS  II.   sp. 

Plate  III,  Figs.  12-13 

1909.     Orthothetes  rubra  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  pi.  12, 
fig.  4  (not  fig.  5). 

Description. — Shell  above  medium  size,  biconvex,  broader  than  long, 
the  binge-line  a  little  less  than  the  greatest  width  of  the  shell,  in  mature 
examples  the  cardinal  extremities  obtusely  angular.  The  dimensions  of 
the  ttolotj  pe  are:  Length  .'!">.">  nun.,  greatest  width  52  mm.,  length  of  hinge- 
line  about  42  mm.,  height  of  cardinal  area  u'  mm. 

I'edicle  valve  very  gently  convex,  most  prominent  in  the  umbonal 
region,  sloping  with  a  very  gentle  curvature  to  the  anterior  and  lateral 
margins,  very  slightly  or  not  at  all  flattened  towards  the  cardinal  ex- 
tremities; mesial  sinus  absent;  beak  blunt,  not  incurved,  cardinal  area 
Mat.  with  sharply  defined  lateral  margins,  sloping  posteriorly  from  the 
hinge-line;  delthyrium  broadly  triangular,  broader  than  high,  closed  by 
a  convex  deltidium  with  a  sinuate  cardinal  margin. 

Brachial  valve  aparently  somewhat  less  convex  than  the  pedicle,  with 
the  surface  flattened  towards  the  cardinal  margin. 

Surface  of  both  valves  marked  by  narrow,  subangular  costa?,  which 
increase  by  implantation,  the  intercostal  spaces  being  wider  than  the  costag 
themselves,  one  or  two  costae  occupying  the  space  of  one  millimeter.  The 
costas  are  crossed  by  rather  strong,  irregularly  developed,  concentric  lines 
of  growth.  Very  fine  concentric  markings  are  faintly  indicated  on  some 
portions  of  the  shell  and  probably  covered  both  valves  when  in  a  perfect 
condition. 

Remarks. — The  holotype  of  this  species  is  a  specimen  preserving  both 
valves  which  have  been  somewhat  crushed  longitudinally.  It  was  at 
first  thought  to  be  an  example  of  S.  rubra,  and  was  originally  illustrated 
as  such,  but  the  difference  in  the  character  of  the  radiating  costse  is  so 
marked  that  it  is  now  described  as  the  type  of  a  distinct  species.  Besides 
the  difference  in  the  radiating  costa?,  the  specimen  is  considerably  larger 
than  any  example  of  S.  rubra  which  has  been  studied.  The  internal 
characters  of  neither  valve  have  been  observed,  and  the  cardinal  margin 
of  the  brachial  valve  has  been  pushed  in  behind  the  cardinal  area  of  the 
pedicle  valve  in  such  a  manner  as  to  hide  the  characters  of  that  portion 
of  that  valve.  It  is  believed  that  the  most  important  distinguishing 
character  of  the  species,  by  means  of  which  it  may  be  separated  from 


SCHUCHERTELLA  00 

other  members  of  the  genus,  is  to  be  found  in  the  comparatively  narrow 
costa:  separated  by  broad  intercostal  spaces. 
Horizon. — Fern  Glen  formation. 

SCHUCHERTELLA  LENS    (White) 

Plate  III,  Figs.  1-8,  9? 

1862.     Streptorhynchns  lens  White,  Proc.  Boston  Soc.  Nat.  Hist,  vol.  9, 

p.  28. 
1892.     Orthothetes  lens  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  1, 

pi.  16,  figs.  12-16. 
1892.     Orthothetes  lens  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  11  A, 

figs.  16-22. 
1894.     Streptorhynchns  lens  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  67,  pi.  39, 

figs  2a-b. 
1904.     Schuchertella  lens  Girty,  Proc.  U.  S.  Nat.  Mus.,  vol.  27,  p.  734. 
1908.     Orthothetes  lens  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 

ser.,  p.  78,  pi.  17,  figs.  37-42. 

Description. — Shell  small,  lenticular  in  form,  broader  than  long,  the 
greatest  width  near  the  mid-length  of  the  shell,  the  hinge-line  usually  a 
little  shorter  than  the  greatest  width,  the  cardinal  extremities  angular. 
The  dimensions  of  two  individuals  are :  length  of  pedicle  valve  14.3  mm. 
and  14.7  mm.,  length  of  brachial  valve  12.9  mm.  and  13.1  mm.,  greatest 
width  16.8  mm.  and  17  mm.,  length  of  hinge-line  14.7  mm.  and  13  mm., 
thickness  6  mm.  and  5.5  mm.,  height  of  cardinal  area  3.8  mm.  and  2.5  mm. 

Pedicle  valve  depressed  convex,  most  prominent  in  the  umbonal  region, 
the  surface  sloping  with  a  gently  convex  curvature  to  the  lateral  and 
anterior  margins,  not  at  all  or  only  very  slightly  depressed  towards  the 
cardinal  extremities;  mesial  sinus  obsolete;  beak  obtusely  pointed,  not 
incurved;  cardinal  area  nearly  flat,  with  sharply  defined  lateral  margins, 
sloping  posteriorly  from  the  hinge-line  at  an  angle  between  115  and  125 
degrees  to  the  plane  of  the  valve ;  delthyrium  broadly  triangular,  as  broad 
or  broader  than  high,  closed  by  a  rather  strongly  convex  deltidium 
which  is  deeply  concave  along  its  cardinal  margin.  Internally  the  apical 
portion  of  the  valve  is  more  or  less  solidified,  the  cardinal  teeth  are  un- 
supported by  dental  plates,  although  the  inner  surface  of  the  valve  is 
thickened  along  each  side  of  the  delthyrium ;  the  muscular  scars  are  of 
moderate  size,  subovate  in  outline  with  their  anterior  margin  lying 
posterior  to  the  middle  of  the  valve,  the  central  adductor  scars  are 
variable  in  their  differentiation,  sometimes  being  only  faintly  defined  and 
again  being  sharply  defined  and  sometimes  raised  anteriorly  above  the 
level  of  the  diductor  scars  on  either  side;  the  inner  margin  of  the  valve 
is  crenulated  laterally  and  anteriorly. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  compressed  towards  the  cardinal  ex- 


56  MISSISSIPPIAN    BRACHIOPODA 

tremities  and  gently  convex  from  the  beak  towards  the  Latera]  and  an- 
terior margins,  the  umbo  qo1  protuberant  beyond  the  cardinal  margin; 
the  mesial  portion  of  the  valve  usually  somewhat  flattened  from  the 
beak  to  the  front  margin,  sometimes  slightly  depressed  to  form  a  very 

shallow,  ill-defined  sinus;  I  he  cardinal  area  very  narrow  with  sharply 
defined  lateral  margins,  forming  an  obtuse  angle  with  that  of  the  opposite 
valve.  Internally  the  cardinal  process  is  short  and  rather  thick,  bifid 
posteriorly,  with  a  chilidinm  adjacent  to  the  cardinal  margin  which 
occupies  the  concavity  in  the  base  of  the  deltidium  of  the  opposite 
valve;  from  either  side  of  the  cardinal  process  the  socket  plates  or  ridges 
diverge  and  are  then  recurved  to  the  cardinal  margin  to  form  the  sockets; 
the  muscular  scars  subovate  in  outline,  reaching  beyond  the  middle  of 
the  valve  and  more  deeply  impressed  than  those  of  the  opposite  valve, 
sometimes  divided  longitudinally  by  a  rather  broad,  slightly  raised 
median  ridge  which  continues  to  the  base  of  the  cardinal  process. 

Surface  of  both  valves  marked  by  sharp,  narrow,  radiating  costae  which 
increase  by  bifurcation  and  intercalation,  about  three  occupy  the  space 
of  one  millimeter  at  the  front  of  mature  shells.  The  costse  are  crossed 
by  fine  concentric  markings,  when  the  surface  is  well  preserved, 
which  give  them  a  crenulated  appearance,  and  by  much  stronger  con- 
centric lines  of  growth  which  are  not  infrequently  crowded  towards  the 
front  of  the  shell. 

//<  marls. — This  species  has  been  selected  by  Girty1  as  the  type  of  his 
genus  Scliuchcrtclla.  It  is  a  very  characteristic  member  of  the  Louisiana 
limestone  fauna,  and  never  attains  a  large  size,  the  largest  individual 
observed  by  the  writer  having  a  length  of  16  mm. 

Horizon. — Louisiana  limestone. 

SCHUCIIERTELLA  RUBRA  Weller 

Plate  III,  Figs.  10-11 

1909.     Orthothetes  rubra  Weller,  Bull.   Geol.   Soc.  Am.,  vol.  20,  p.   294, 
pi.  12,  fig.  5  (not  fig.  4). 

Description. — Shell  of  medium  size  or  a  little  larger,  biconvex,  broader 
than  long,  the  greatest  width  near  the  mid-length,  the  hinge-line  straight, 
a  little  shorter  than  the  greatest  width,  the  cardinal  extremities  angular, 
the  central  portion  of  the  anterior  margin  nearly  straight  or  slightly 
emarginate.  The  dimensions  of  a  somewhat  crushed  specimen  preserving 
both  valves  are:  length  of  pedicle  valve  25.3  mm.,  length  of  brachial 
valve  24  mm.,  greatest  width  36  mm.,  length  of  hinge-line  32  mm.,  thick- 
ness approximately  10  mm.,  height  of  cardinal  area  approximately  3  mm. 

Pedicle  valve  gently  convex,  greatest  convexity  posterior  to  the  middle, 

iProc.  U.  S.  Nat.  Mus.,  vol.  27,  p.  734  (1904). 


SCHTJCHERTKU.A  57 

the  surface  slightly  compressed  towards  the  cardinal  extremities ;  median 
portion  of  the  valve  a  little  flattened  anterior  to  the  middle  but  not  de- 
pressed in  a  mesial  sinus;  beak  apparently  obtusely  angular,  but  slightly 
protuberant  beyond  the  cardinal  margin ;  cardinal  area  rather  low,  ap- 
parently flat  and  lying  nearly  at  a  right  angle  to  the  plane  of  the  valve, 
the  lateral  margins  sharply  defined  and  angular,  sloping  in  nearly 
straight  or  slightly  concave  lines  from  the  beak  to  the  cardinal  extrem- 
ities ;  the  delthyrium  broadly  triangular,  its  apical  portion  closed  by  a 
convex  deltidium.  Internally  the  dental  plates  are  apparently  obsolete; 
the  flabellate  muscular  scars  are  of  medium  size,  but  are  illdefined  and 
only  slightly  impressed. 

Brachial  valve  about  equally  convex  with  the  pedicle,  but  with  the 
greatest  convexity  situated  farther  towards  the  front,  apparently  anterior 
to  the  middle  in  the  type  specimen,  the  surface  compressed  towards  the 
cardinal  extremities,  the  umbonal  region  flattened;  the  mesial  portion  of 
the  valve  depressed  in  a  shallow  and  rather  broad,  ill-defined  mesial  sinus ; 
the  beak  inconspicuous.  Internal  characters  not  observed,  although  the 
posterior  extremity  of  a  rather  broad  cardinal  process  is  exhibited 
in  the  type  specimen. 

Surface  of  both  valves  marked  by  fine,  subangular,  radiating  costa? 
which  are  slightly  irregular  in  size,  separated  by  rather  deep  intercostal 
furrows,  about  three  occupying  the  space  of  1  mm.  Crossing  the  costas 
are  fine,  concentric  markings  which  seem  to  be  more  conspicuous  towards 
the  cardinal  extremities,  in  which  portion  of  the  shell  the  radiating 
costse  are  minutely  serrate  by  reason  of  the  crossing  of  the  concentric 
lines.  A  few  rather  faint  concentric  lines  of  growth  are  present  upon 
the  body  of  the  shell,  but  in  old  examples  they  become  very  strong  near 
the  margins  of  the  valves. 

Remarks. — This  species  resembles  S.  lens  from  the  Louisiana  limestone, 
but  it  attains  a  much  larger  size,  is  proportionally  broader,  and  is  marked 
by  somewhat  finer  radiating  costag.  The  smaller,  immature  examples  of 
about  the  average  size  of  8.  lens  may  be  distinguished  from  that  species 
by  their  form  and  costa?. 

Horizon. — Fern  Glen  formation. 

Schuchertelea  costatula   (Hall  and  Clarke) 

Plate  II,  Figs.  19-22 

1892.     Derbya   (?)   costatula  Hall    and    Clarke,  Pal.  N.  Y.,  vol.  8,  pt,  1. 

p.  346,  pi.  11B,  figs.  16-17. 
1897.     Derbya  ( t)  costatula  Hall,  14th  Ann.  Rep.  N.  Y.  State  Geol.,  p.  346, 
pi.  5,  fig.  9. 

Description. — Shell  small,  broader  than  long,  the  hinge-line  as  long  or 
nearly  as  long  as  the  greatest  width  of  the  shell,  the  cardinal  extremities 
angular.     The  dimensions  of  the  holotype  are:    length  of  pedicle  valve 


58  viississippian  brachiopoda 

li'  linn..  Length  of  brachial  valve  !).(>  mm.,  greatest  width  12.4  mm.,  length 
of  hinge-line  10.8  mum.,  height  of  cardinal  area,  2.N  mm.,  thickness  5.6  mm. 

Pedicle  valve  somewhat  distorted,  moderately  convex,  most  prominent 
posteriorly,  the  surface  a  little  compressed  towards  the  cardinal  ex- 
tremities, with  no  mesial  sinus;  the  beak  pointed,  extending  conspicuously 
beyond  the  cardinal  margin  posteriorly;  cardinal  area  of  moderate  height, 
flat,  inclined  posteriorly,  the  lateral  margins  sharply  defined  ami  angular, 
sloping  in  nearly  straight,  slightly  concave  or  slightly  convex  lines  from 
the  beak  to  the  cardinal  extremities;  the  dell  hy  rium  broadly  triangular, 
closed  by  a  convex  dell  idiiim.  Internally  the  hinge-teeth  are  supported 
by  short  dental  lamellae,  no  median  septum  present. 

Brachial  valve  rather  strongly  convex,  the  greatest  convexity  near  the 
middle,  compressed  towards  the  cardinal  extremities;  the  umbonal  region 
prominent,  but  not  protuberant  posteriorly  beyond  the  cardinal  margin, 
the  surface  curvature  more  gentle  towards  the  lateral  and  anterior 
margins. 

The  surface  markings  of  both  valves  consist  of  a  series  of  rather  strong 
radiating  costse  from  one  to  two  millimeters  apart,  which  originate  in 
the  umbonal  region  and  which  are  absent  towards  the  cardinal  extrem- 
ities, between  the  coarser  costre  and  extending  to  the  cardinal  extremities, 
the  surface  is  covered  by  much  finer  radiating  costse.  The  surface  also 
marked  by  regular,  concentric  lines  of  growth  of  moderate  strength. 

B<  murks. — This  species  was  originally  described  as  a  member  of  the 
genus  Derbya,  with  a  query,  by  Hall  and  Clarke.  The  holotype  of  the 
species  showTs  neither  the  presence  or  absence  of  a  median  septum  in  the 
pedicle  valve,  but  another  specimen,  a  pedicle  valve  with  a  perfectly  clean 
interior,  from  the  same  locality  as  the  holotype,  shows  conclusively  that 
no  such  septum  is  present.  The  dental  lamellse  in  the  same  specimen  are 
better  developed  than  in  the  typical  Schuchcrtella  where  they  are  reduced 
to  mere  thickenings  of  the  inner  surface  of  the  valve  along  the  margins 
of  the  delthyrium,  being  distinct  plates,  although  very  short.  In  this 
character,  then,  the  species  resembles  the  members  of  the  genus 
Schellwienella,  but  it  does  not  possess  the  resupinate  form  of  typical 
members  of  that  genus.  The  species  is,  therefore,  intermediate  in  its 
characters  between  these  two  genera,  and  is  placed  in  Schuchertella  some- 
what arbitrarily. 

The  species  is  especially  characterized  by  the  strong  radiating  costae 
which  occur  at  intervals,  with  the  much  finer  ones  between.  Occasionally 
specimens  of  the  truly  septate  Orthotetes  kaskaskiensis  exhibit  this  same 
characteristic,  though  not  to  such  a  conspicuous  degree,  but  that  species 
is  always  a  much  larger  shell  in  its  adult  condition,  than  the  largest  ex- 
amples of  8.  costahda  which  have  been  observed. 

Horizon. — Chester  group. 


SCHKLLWIENELLA  59 

Genus  SCHELLWIENELLA  Thomas 

Description. — Shell  resupinate,  the  pedicle  valve  flat  or  concave,  the 
brachial  valve  convex,  the  hinge-line  equaling,  less  than  or  greater  than 
the  greatest  width  of  the  shell  in  front,  the  lateral  and  anterior  margins 
rounded.  Cardinal  area  of  the  pedicle  valve  variable  in  height,  differen- 
tiated into  a  primary  and  a  secondary  area  as  in  Scliuchertella,  and  with 
the  deltidium  closing  the  delthyrium  to  the  apex.  Internally  the  dental 
lamellae  are  short  and  rather  widely  divergent,  and  a  median  septum  is 
absent.  The  brachial  valve  is  convex,  often  strongly  so,  with  no  cardinal 
area. 

Remarks. — 8.  inflata  may  be  considered  as  atypical  American  representa- 
tive of  this  genus,  it  being  a  species  in  which  both  the  resupinate  shell  and 
the  short  and  widely  divergent  dental  lamellae  have  been  clearly  recog- 
nized, these  two  characters  being  the  essential  features  by  means  of  which 
members  of  this  genus  may  be  differentiated  from  Scliuchertella.  In  prac- 
tice the  resupinate  form  of  the  shell,  viz.,  the  concave  pedicle  valve,  will 
doubtless  be  most  commonly  used  for  distinguishing  the  genus.  Among 
the  examples  studied  in  which  the  characters  of  the  dental  lamella?  can  be 
determined  there  seems  to  be  some  variation  in  the  strength  of  their  de- 
velopment, in  some  instances  these  lamella?  being  but  little  or  not  at  all 
different  from  those  of  Schuchertella.  The  two  genera  are  closely  allied 
and  it  is  not  surprising  that  there  should  be  a  more  or  less  complete 
mtergradation  in  the  character  of  the  dental  lamella?,  but  in  no  case  among 
the  specimens  here  studied  has  there  been  any  hesitation  as  to  the  genus 
in  which  any  one  should  be  placed  on  the  basis  of  the  form  of  the  pedicle 
valve. 

Schellwienella  inplata  (White  and  Whitfield) 

Plate  IV,  Figs.  7-12 ;  Plate  LXXXIII,  Fig.  11 

1862.     Streptorhynchus  inflatus  White  and  Whitfield,  Proc.  Boston  Soc.  Nat. 

Hist.,  vol.  8,  p.  293. 
1877.     Streptorhynchus  inflatus  Hall  and  Whitfield,  TJ.  S.  Geol.  Expl.,  40th 

Par.,  vol.  4,  p.  253,  pi.  4,  fig.  3. 
1883.     Streptorhynchus  wquivalvis  Hall,  Rep.  N.  Y.  State  Geol.,  for  1882, 

pi.  (HA)  42,  figs.  24,  25. 
1892.     Orthothetes  inflatus  Hall  and  Clarke,  Pal.  N.  T.,  vol.  8,  pt.  1.  pi.  9A, 

figs.  24,  25. 
1901.     Orthothetes  inflatus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 

pp.  181  and  195,  pi.  16,  figs.  2-3,  and  pi.  19,  figs.  10-12. 

Description. — Shell  concavo-convex,  of  medium  size  or  larger,  usually 
subelliptical  in  outline  and  broader  than  long  with  the  greatest  width 
near  or  posterior  to  the  mid-length,  the  hinge-line  a  little  shorter  than  the 
greatest  width,  the  cardinal  extremities  obtusely  angular  or  a  little 
rounded.     The  dimensions  of  a  nearly  complete  example,  one  of  the  co- 


60  MISSISSCPP1AN    BEACHIOPODA 

types  of  the  species,  which  is  exceptionally  elongate  in  form,  are:  length 
of  pedicle  valve  28.5  nun.,  length  of  brachial  valve  27.3  mm.,  greatest 
width  27.8  nun.,  length  of  hinge-line  2<>  mm.,  height  of  cardinal  area  8.7 
nun.,  convexity  of  brachial  v;ilve  14  mm.  The  dimensions  of  a  detached 
brachial  valve  from  the  typical  locality  are:  length  25.6  mm.,  width  ',Y.\ 
mm.,  length  of  hinge-line  ±30  mm.,  convexity  10  mm. 

Pedicle  valve  concave  in  general  contour  with  the  surface  flattened  or 
slightly  convex  towards  the  cardinal  extremities  and  the  umbonal  region 
slightly  convex  over  a  small  area,  the  greatest  concavity  near  or  anterior 
to  the  middle;  mesial  sinus  obsolete;  beak  small,  pointed,  nearly  erect, 
sometimes  a  little  distorted  or  recurved;  cardinal  area  of  moderate  height 
in  the  only  specimen  in  which  it  has  been  observed,  convex  from  the 
cardinal  margin  to  the  apex  with  the  lower  portion  sloping  posteriorly 
from  the  hinge-line  at  an  angle  of  about  110  degrees,  the  lateral  margins 
sharply  angular,  sloping  from  the  beak  to  the  cardinal  extremities  in 
slightly  flexuous  lines  due  to  the  distortion  of  the  beak,  the  delthyrium 
narrowly  triangular,  much  higher  than  wide. 

Brachial  valve  strongly  convex,  the  greatest  convexity  near  or  poste- 
rior to  the  middle,  the  umbonal  region  prominent  and  usually  somewhat 
protuberant  posteriorly  beyond  the  hinge-line,  the  surface  curving  more 
abruptly  from  the  point  of  greatest  convexity  to  the  cardinal  margin  and 
a  little  more  gently  to  the  lateral  and  anterior  margins,  compressed  and 
somewhat  auriculate  towards  the  cardinal  extremities;  mesial  portion  of 
the  valve  not  differentiated ;  beak  inconspicuous. 

Surface  of  both  valves  marked  by  fine,  narrowly  rounded  or  subangular 
costa>,  somewhat  irregular  in  size,  from  two  to  four  occupy  the  space  of 
one  millimeter.  Concentric  markings  of  the  shell  inconspicuous;  in  no 
case  is  the  surface  of  the  shell  preserved  so  as  to  show  the  minute  mark- 
ings, and  the  stronger  lines  of  growth  are  limited  to  a  few  more  or  less  in- 
conspicuous, wrinkle-like  markings  which  are  often  nearly  or  quite 
obsolete. 

Bemarks. — The  types  of  this  species  are  mostly  from  the  uppermost,  mag- 
nesian  limestone  layer  of  the  Kinderhook,  at  Burlington,  Iowa,  although 
some  examples  from  the  Kinderhook  oolite  of  the  same  locality  are  in- 
cluded in  the  type  lot.  The  only  specimen  retaining  both  valves  in  artic- 
ulation is  from  the  magnesian  limestone  layer  and  it  is  from  that  bed  that 
the  most  of  the  specimens  in  more  recent  collections  have  been  secured. 
The  specimens  most  commonly  found,  both  at  the  type  locality  and  else- 
where, are  detached  brachial  valves.  The  only  specimen  retaining  both 
valves  in  articulation  which  has  been  observed,  and  the  only  one  in  which 
the  length  is  greater  than  the  width,  is  one  of  the  types  already  mentioned, 
it  alone  has  been  the  source  of  the  description  of  the  pedicle  valve  given 
above ;  not  enough  specimens  have  been  examined  to  determine  whether 
or  not  the  beak  is  commonly  distorted  as  in  that  specimen,  or  whether 


SCHELLWIENELLA  61 

the  cardinal  area  is  commonly  convex.  An  internal  cast  of  a  pedicle 
valve  from  the  same  horizon  and  locality,  probably  a  member  of  this 
species,  does  not  have  a  distorted  beak  and  has  a  flat  cardinal  area  which 
slopes  posteriorly  from  the  hinge-line  at  an  angle  of  about  115  degrees ;  it 
also  shows  the  presence  of  short  but  distinct  dental  plates  and  a  scarcely 
defined,  flabellate  muscular  scar. 

The  pedicle  valve  of  this  species,  so  far  as  it  has  been  observed,  re- 
sembles that  of  8.  planumbona,  but  it  is  probably  more  often  distorted  at 
the  beak  than  that  species  and  usually  has  more  conspicuous  lines  of 
growth.  It  is  probably  true,  however,  that  some  specimens  of  the  pedicle 
valve  of  S.  planumbona  were  included  by  White  and  Whitfield  among  the 
types  of  this  species.  The  brachial  valves  of  the  two  species  are  entirely 
different,  the  umbonal  region  of  this  one  being  very  prominent  and  some- 
what protuberant  beyond  the  cardinal  margin,  while  the  same  region  in 
S.  planumbona  is  very  gently  convex,  the  slope  to  the  anterior  margin  of 
the  shell  being  more  abrupt  than  that  to  the  cardinal  margin. 

Horizon.— Kinderhook. 

SCHELLWIEJNTELLA    INiEQUALIS    (Hall) 

Plate  III,  Figs.  14-16 

1858.  Orthis  inequalis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  490,  pi.  2,  figs.  6a-c. 
1865.     Streptorhynchus  inequalis  Winchell,  Proc.  Acad.  Nat.   Sci.,  Phil., 

p.  117. 
1870.     Hemipronites  inequalis  Winchell,    Proc.   Am.   Phil.    Soc,   vol.    11, 

p.  251. 
1877.     Streptorhynchus  equivalvis  Hall  and  Whitfield,  U.  S.  Geol.  Expl., 

40th  Par.,  vol.  4,  p.  252,  pi.  4,  figs.  1.  2. 
1883.     Streptorhynchus  cequivalvis  Hall,  Rep.  N.  Y.  State  Geol.  for  1882, 

pi.  (11A)  42,  figs.  20-23. 
1892.     Orthothetes  in/equalis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  9 A,  figs.  20-23. 

1899.  Orthothetes  incequalis  Girty,  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p.  522, 

pi.  68,  fig.  3a. 

1900.  Orthothetes  imzqioalis  Weller,  trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  66,  pi.  1,  fig.  18. 

1901.  Orthothetes  inwqualis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 

pp.  159  and  195,  pi.  14,  figs.  16-18,  and  pi.  19,  fig.  9. 
1903.     Orthothetes  incequalis  Girtv,  Prof.  Paper  IT.  S.  Geol.  Survey  No.  16, 
p.  276. 

Description.  —  Shell  concavo-convex,  of  about  medium  size,  wider  than 
long,  the  greatest  width  near  or  in  front  of  the  mid-length,  the  hinge-line 
a  little  shorter  than  the  greatest  width,  the  cardinal  extremities  angular. 
The  dimensions  of  a  large,  nearly  complete  pedicle  valve  are :  length  23.7 
mm.,  greatest  width  31.4  mm.,  length  of  hinge-line  30  mm.  The  dimen- 
sions of  a  brachial  valve  are :  length  18.5  mm.,  width  22  mm.,  length  of 
hinge-line  18.5  mm.,  convexity  6.5  mm. 


02  \i  ISSISSIITIAN    BEACHIOPODA 

Pedicle  valve  nearly  Hal  throughoul  in  immature  specimens,  becoming 
concave  as  ii  approaches  maturity,  the  curvature  beginning  a1  a  little 
more  than  two-thirds  the  length  of  the  shell  Erom  the  beak  in  the  speci- 
men whose  dimensions  are  given  above,  towards  the  cardinal  extremities 
the  surface  is  very  gently  convex  as  it  approaches  the  cardinal  margin; 
mesial  sinus  obsolete;  the  beak  inconspicuous,  in  the  internal  easts  scarce- 
ly extended  beyond  the  straight  or  nearly  straight  cardinal  margin  of  the 
valve;  cardinal  area  narrow,  lying  at  nearly  a  right  angle  to  the  plane  of 
the  valve,  the  lateral  margins  angular,  the  two  sides  of  the  beak  being  in 
nearly  a  straight  line;  the  delthyrium  broadly  triangular.  Internally 
Ihr  hinge-teeth  are  supported  by  thickened  ridges  on  the  inner  surface 
along  each  margin  of  the  delthyrium,  which  can  scarcely  be  designated  as 
dental  plates;  the  muscular  scars  obscure  or  poorly  defined. 

Brachial  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  curving  more  abruptly  towards  the  cardinal 
margin,  the  cardinal  extremities  compressed  and  subauriculate,  the  um- 
bonal  region  prominent  and  projecting  somewhat  beyond  the  cardinal 
margin;  the  mesial  portion  of  the  valve  flattened  or  depressed  in  a  shal- 
low, ill-defined  sinus  which  in  the  casts  is  better  developed  near  the  beak ; 
the  beak  not  conspicuous,  somewhat  incurved.  Internal  characters  not 
well  exhibited  in  any  of  the  specimens. 

Surface  of  both  valves  marked  by  radiating  costae  which,  on  the  casts, 
are  subangular  and  irregular  in  size,  although  not  distinctly  alternating, 
those  of  the  pedicle  valve  being  more  regular  than  those  of  the  brachial, 
from  two  to  four  occupying  the  space  of  1  mm.  at  the  margin  of  the 
valves ;  the  costa?  are  apparently  more  numerous  at  the  margin  than  fur- 
ther  back,  the  additional  ones  being  added  close  to  the  margin  and  being 
in  the  nature  of  crenulations  of  the  inner  margin  which  would  not  be 
shown  on  the  external  surface,  rarely  more  than  two  in  the  space  of  1  mm. 
at  the  margin  on  the  outside.  The  cost*  are  crossed  by  concentric  lines 
of  growth  which  are  usually  restricted  to  the  region  near  the  margin. 

Remarks.— This  species  is  known  only  from  specimens  preserved  as  in- 
ternal casts  in  a  fine-grained  yellow  sandstone,  which  do  not  preserve  the 
minute  surface  markings.  In  no  case  have  the  two  valves  been  seen  in 
articulation,  but  the  pedicle  and  brachial  valves  here  described  occur  in 
such  association  as  to  make  it  almost  certain  that  they  are  parts  of  the 
same  species.  The  species  is  especially  characterized  by  the  slight  mesial 
sinus  in  the  brachial  valve,  by  the  flatness  of  the  pedicle  valve  to  near  the 
margin  where  the  concavity  begins,  and  by  the  straight  cardinal  margin 
of  the  pedicle  valve  and  narrow  cardinal  area. 

Horizon. — Kinderhook. 


SCHELLWIENELLA  63 

SCHELLWIENELLA  CRENULICOSTATA  n.  sp. 

Plate  III,  Figs.  17-18 

Description. — Shell  concavo-convex,  a  little  above  medium  size,  broader 
than  long,  the  greatest  width  near  or  posterior  to  the  mid-length,  the 
hinge-line  a  little  shorter  than  the  greatest  width,  the  cardinal  extremities 
angular.  The  dimensions  of  a  very  perfect  pedicle  valve  are:  length  25.8 
mm.,  greatest  width  35  mm.,  length  of  hinge-line  30  mm.,  height  of  car- 
dinal area  2.6  mm. 

Pedicle  valve  concave,  the  greatest  concavity  near  the  middle,  the 
surface  flattened  towards  the  cardinal  extremities,  a  small  umbonal  region 
rather  abruptly  elevated  from  the  general  surface ;  mesial  sinus  obsolete ; 
the  beak  small,  nearly  erect ;  cardinal  area  narrow,  lying  at  nearly  a  right 
angle  to  the  jdane  of  the  valve,  the  lateral  margins  sharply  defined,  nearly 
straight  or  gently  convex  from  the  cardinal  extremities  nearly  to  the  beak, 
where  they  become  concave  and  curve  up  rather  abruptly  to  the  apex 
of  the  valve,  the  lateral  margins  on  the  two  sides  of  the  beak  lying  in 
essentially  a  straight  line ;  delthyrium  broadly  triangular,  twice  or  more 
than  twice  as  wide  as  high  with  a  convex  deltidium  closing  the  apical 
portion.  Internally  a  pair  of  widely  divergent  hinge-teeth  of  moderate 
size  are  present ;  the  other  internal  characters  not  observed  but  the  dental 
plates  are  probably  restricted  to  ridge-like  thickenings  of  the  inner  sur- 
face of  the  shell  at  each  side  of  the  delthyrium. 

Brachial  valve  not  observed. 

Surface  of  the  shell  marked  by  fine,  uniform,  regularly  dividing,  rounded 
costae,  about  four  or  sometimes  five  of  which  occupy  the  space  of  1  mm., 
with  the  intercostal  furrows  narrower  than  the  costae.  Crossing  the 
cost*  there  are  fine,  concentric  markings,  becoming  more  conspicuous 
beyond  the  middle  of  the  valve  where  they  divide  the  summits  of  the 
radiating  costae  into  a  series  of  crenulations.  Besides  the  fine  concentric 
markings  there  are  a  few  much  stronger,  concentric  lines  of  growth 
which  are  more  conspicuous  towards  the  outer  margin. 

Ii'i  marks. — This  species  has  been  described  almost  exclusively  from  a 
very  perfect  pedicle  valve  from  the  Kinderhook  oolite  at  Burlington, 
Iowa,  but  it  is  recognized  also,  from  the  pedicle  valve  alone,  in  the  sub- 
jacent yellow  sandstone  at  the  same  locality.  In  general  outline  the  shell 
is  not  greatly  different  from  S.  infldtus  or  S.  incequalis.  It  differs  from 
both  these  species  in  the  size  and  form  of  the  radiating  costas.  The  pedicle 
valve  of  the  species  may  be  distinguished  from  that  of  S.  inflatus  by  its 
much  narrower  cardinal  area,  by  the  nearly  straight  line  formed  by  the 
two  lateral  margins  of  the  area,  and  by  the  small,  abruptly  elevated 
umbonal  region  of  the  valve.  From  8.  incequalis  the  species  differs,  in 
addition  to  the  different  character  of  the  costae,  in  the  greater  concavity 


1)4  MISSISSIPPIAN    BRACHIOPODA 

of  the  pedicle  valve.  Hie  concavity  being  distributed  through  the  entire 
length  of  the  valve,  and  in  the  abruptly  elevated  umbonal  region;  the  two 
species  are  similar  in  their  narrow  cardinal  areas,  the  two  lateral  margins 
of  which  form  nearly  a  straight  line, 
Horizon. —  Kindcrhook. 

SciiKU-WlKNKU.A   CHOUTEAUENSIS   n.  sp. 
Plate  VII,  Figs.  5-8 

Description, — Shell  of  medium  size  or  a  little  larger,  broader  than  long, 
the  hinge-line  nearly  or  quite  equaling  the  greatest,  width,  the  cardinal 
extremities  angular,  the  lateral  margins  nearly  straight  or  gently  convex 
posteriorly,  becoming  more  convex  anteriorly  and  rounding  without  in- 
terruption into  the  convex  anterior  margin.  The  dimensions  of  a  nearly 
complete  specimen  are:  length  of  pedicle  valve  23  mm.,  length  of  brachial 
valve  21  mm.,  greatest  width  27.5  mm.,  length  of  hinge-line  24.5  mm., 
convexity  of  brachial  valve  4.8  mm.,  height  of  cardinal  area  3.8  mm. 

Pedicle  valve  concave  or  sometimes  nearly  flat,  most  prominent  on  the 
umbo  which  is  raised  above  the  remaining  surface  of  the  valve ;  mesial 
sinus  obsolete;  beak  obtusely  angular,  erect;  cardinal  area  of  moderate 
width,  flat,  with  sharply  angular  lateral  margins  which  slope  from  the 
beak  to  the  cardinal  extremities  in  nearly  straight  lines;  the  delthyrium 
wider  than  high,  closed  by  a  convex  deltidium  with  a  concave  cardinal 
margin.    Internal  characters  not  observed. 

Brachial  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  curving  gently  from  the  highest  point  to  the  lateral 
and  anterior  margins,  a  little  more  abruptly  to  the  cardinal  margin, 
somewhat  compressed  towards  the  cardinal  extremities ;  mesial  fold 
obsolete ;  beak  inconspicuous,  not  extended  beyond  the  cardinal  margin ; 
cardinal  area  very  narrow,  making  an  obtuse  angle  with  that  of  the 
opposite  valve,  the  middle  of  the  hinge-line  marked  by  the  rather  prom- 
inent posterior  extremity  of  the  cardinal  process  which  fills  the  concave 
cardinal  excavation  of  the  deltidium  of  the  opposite  valve.  Internal 
characters  not  observed. 

Surface  of  both  valves  marked  by  rather  coarse  radiating  costre  which 
are  similar  on  the  two  valves,  about  two  occupying  the  space  of  one 
millimeter.  The  costae  are  crossed  by  regular,  strong,  irregularly  distrib- 
uted, concentric  lines  of  growth  which  are  commonly  more  crowded  to- 
wards the  front  of  the  shell. 

Remarks. — This  species  from  the  Chouteau  limestone  is  perhaps  more 
closely  similar  to  8.  incequalis  than  to  any  other  species  of  the  genus  here 
considered,  but  it  is  a  more  coarsely  costate  shell  than  that  one. 

Horizon. — Chouteau  limestone. 


SCHELLWIENELLA  65 

SCHELLWIENELLA   PLANUMBONA   11.    sp. 

Plate  III,  Figs.  19-22 

1901.     Orthothetes  sp.  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11,  p.  181, 
pi.  16,  fig.  1. 

Description.— Shell  above  medium  size,  subelliptieal  in  outline,  usually 
perfectly  symmetrical,  broader  than  long,  the  greatest  width  near  the 
mid-length,  the  hinge-line  a  little  shorter  than  the  greatest  width,  the 
cardinal  extremities  angular.  The  dimensions  of  two  nearly  complete 
pedicle  valves  are :  length  39.5  mm.  and  31  mm.,  width  49  mm.  and  38 
mm.,  length  of  hinge-line  40  mm.  and  34.2  mm.,  height  of  cardinal  area 
7.8  nun.  and  5.8  mm.  The  dimensions  of  an  imperfect  brachial  valve  are: 
length  28  mm.,  width  31  mm.,  length  of  hinge-line  28  mm.,  convexity  8.5 
mm. 

Pedicle  valve  concave  in  general  contour,  with  the  small  umbonal 
region  depressed  convex,  and  the  surface  towards  the  cardinal  extrem- 
ities flattened  or  gently  convex;  mesial  sinus  obsolete;  the  beak  obtusely 
pointed,  inclined  posteriorly;  cardinal  area  flat,  of  moderate  height,  slop- 
ing posteriorly  from  the  hinge-line  at  an  angle  of  about  110  degrees,  the 
lateral  margins  sharply  angular,  sloping  in  nearly  straight  lines  from  the 
beak  to  the  cardinal  extremities ;  the  delthyrium  about  as  wide  or  a  little 
wider  than  high,  its  apical  portion  covered  by  a  strongly  convex  deltidium 
which  does  not  reach  much  beyond  the  mid-height  of  the  area,  the  lower 
portion  apparently  being  occupied  by  the  posterior  extremity  of  the 
cardinal  process  of  the  opposite  valve.  The  internal  features  of  the 
valve  are  not  well  shown  in  any  of  the  specimens,  but  the  dental  plates 
seem  to  be  poorly  developed,  being  little  more  than  thickened  ridges  on 
each  side  of  the  delthyrium;  the  muscular  scars  apparently  ill-defined;  the 
inner  surface  of  the  valve  erenulate  along  the  lateral  and  anterior 
margins. 

Brachial  valve  convex  with  the  greatest  convexity  near  or  anterior  to 
the  middle;  the  surface  curving  gently  from  the  highest  point  to  the 
cardinal  margin  and  more  abruptly  to  the  anterior  and  antero-lateral 
margins,  the  umbonal  region  flattened  or  depressed-convex,  the  surface 
compressed  towards  the  cardinal  extremities ;  mesial  portion  of  the  valve 
not  differentiated ;  the  beak  inconspicuous,  not  extended  beyond  the  car- 
dinal margin.     Internal  features  of  the  valve  not  observed. 

Surface  of  both  valves  marked  by  fine,  rounded,  radiating  costa>  which 
increase  by  bifurcation  and  by  implantation,  from  two  to  four  occupying 
the  space  of  one  millimeter.  Distinct  concentric  lines  of  growth  are  not 
commonly  present  upon  either  valve. 

Remarks. — This  species  is  the  most  common  form  of  the  genus  occurring 
in  the  Kinderhook  oolite  at  Burlington,  Iowa.    It  is  especially  character- 

—3 


66 


MISNISSIITIAN     ISUACIIHiroDA 


ized  by  the  form  of  the  brachial  valve  which  lias  its  greatest  convexity 
farther  forward  than  is  usual  in  members  of  the  genus,  so  that  the 
curvature  to  the  anterior  margin  is  somewhat  more  abrupt  than  to  the 
binge-line.  The  pedicle  valve  resembles  that  of  8.  inflatus,  but  the  beak 
seems  to  be  more  depressed,  the  brachial  valves  of  the  two  species,  how- 
ever,  are  very  different.  The  usual  absence  of  concentric  growth  lines 
is  a  noticeable  character  of  the  species.  The  two  valves  have  not  been 
observed  in  articulation,  but  both  occur  in  such  close  association  in  the 
Limestone  as  to  leave  no  doubt  as  to  their  being  parts  of  the  same  species. 
Horizon. — Kinderhook. 


SCHELLWIENELLA   AI.TKRNATA  n.  sp. 
Plate  IV,  Fig.  6 

Description, — Shell  rather  large,  broader  than  long,  the  hinge-line  a 
little  shorter  than  the  greatest  width,  the  cardinal  extremities  angular. 
The  dimensions  of  a  nearly  complete  brachial  valve  are:  length  41.5  mm., 
width  57  mm.,  length  of  hinge-line  51.5  mm.,  convexity  11.8  mm. 

Pedicle  valve  not  observed. 

Brachial  valve  convex,  the  greatest  convexity  anterior  to  the  middle, 
the  surface  curving  with  a  more  abrupt  slope  to  the  front  margin  than 
to  the  cardinal  margin,  compressed  and  subauricular  towards  the  cardinal 
extremities,  the  umbonal  region  depressed  convex  or  nearly  flat;  the 
mesial  portion  of  the  valve  somewhat  flattened  from  the  beak  to  the  front 
margin  but  not  distinctly  differentiated  from  the  general  curvature  of 
the  surface ;  the  beak  inconspicuous,  not  produced  beyond  the  cardinal 
margin. 

Surface  of  the  shell  marked  by  a  series  of  stronger,  rounded,  radiating 
costae,  averaging  a  little  less  than  1  mm.  apart  at  the  shell  margin,  alter- 
nating with  which  there  are  usually  very  much  finer  and  more  angular 
eostse.  The  costse  are  crossed  by  fine,  concentric  markings  which  are 
stronger  in  the  intercostal  furrows,  being  nearly  obsolete  on  the  summits 
of  the  costa?.  A  few  stronger  concentric  lines  of  growth  are  also  present 
at  intervals. 

Remarks. — This  species  is  based  upon  a  single,  nearly  complete  brachial 
valve,  no  pedicle  valve  having  been  found  which  can  be  associated  with 
it.  This  valve  somewhat  resembles  8.  planumboiia  in  its  distinctly  flat- 
tened umbonal  region,  but  it  is  proportionally  broader,  besides  having 
distinctly  different  surface  markings.  The  distinctly  alternating  costa? 
with  the  concentric  markings  stronger  in  the  intercostal  furrows  are 
characters  not  shared  with  any  other  species  of  the  genus  here  described. 

In  the  absence  of  the  pedicle  valve  it  is  not  possible  to  determine  cer- 
tainly the  true  generic  relations  of  this  species,  and  it  may  eventually 
prove  to  be  a  member  of  the  genus  Schuchertella.     The  species  has  been 


SCHELLWIENELLA  67 

placed  in  Schellwu  nella  because  its  relationships  seem  to  be  closer  to  S. 
planumbona  than  to  any  other  species,  and  that  form  has  been  definitely 
established   as   being   one   of  the   more   typical   members   of  the   genus 
Schcllw-ienella  in  our  faunas. 
Horizon. — Burlington  limestone. 

SCHELLWIENELLA  BIRLINGTONENSIS  n.  sp. 

Plate  IV,  Figs.  1,  2 

Description. — Shell  large,  subsemielliptical  in  outline,  wider  than  long, 
the  greatest  width  along  the  hinge  line,  the  cardinal  extremities  angular 
and  semiauriculate,  the  lateral  margins  gently  concave  in  front  of  the 
cardinal  extremities,  becoming  gently  convex  anteriorly  and  then  curving 
without  interruption  into  the  anterior  margin  which,  with  the  convex 
portions  of  the  lateral  margins,  is  nearly  semicircular.  The  dimensions  of 
a  pedicle  valve  are :  length  64.5  mm.,  width  along  hinge-line  90  mm., 
height  of  cardinal  area  21.5  mm.  The  dimensions  of  a  brachial  valve  are : 
length  47  mm.,  width  along  hinge  line  ±65  mm. 

Pedicle  valve  gently  concave  along  a  line  from  the  beak  to  near  the 
front  margin,  beyond  which  it  becomes  convex,  the  surface  nearly  flat 
towards  the  cardinal  extremities  and  convex  in  a  comparatively  narrow 
marginal  band  along  the  lateral  and  anterior  margins,  most  prominent  in 
the  umbonal  region  close  to  the  cardinal  margin ;  mesial  sinus  obsolete ; 
the  beak  erect,  very  broadly  obtuse ;  cardinal  area  high  and  flat,  sloping 
posteriorly  from  the  hinge-line  at  an  angle  of  about  120  degrees  to  the 
plane  of  the  valve,  the  lateral  margins  sharply  angular,  sloping  from  the 
beak  to  the  cardinal  extremities  in  a  convex  curve  which  is  gentle  until 
it  approaches  the  extremities  where  it  becomes  much  more  abrupt ;  the 
delthyrium  higher  than  wide,  closed  by  a  deltidium.  Internal  characters 
not  observed. 

Brachial  valve  convex,  the  greatest  convexity  probably  near  the  middle, 
the  surface  compressed  towards  the  cardinal  extremities,  the  umbo  a 
little  prominent  but  not  protuberant  beyond  the  cardinal  margin ;  mesial 
fold  obsolete ;  beak  scarcely  differentiated,  not  extending  beyond  the 
cardinal  margin.  Internal  characters  not  observed  beyond  the  posterior 
extremity  of  the  cardinal  process  which  is  large,  about  twice  as  wide  as 
high,  and  deeply  bifid. 

Surface  of  both  valves  marked  by  regular,  rounded,  radiating  costai 
about  two  of  which  occupy  the  space  of  one  millimeter  near  the  margin 
of  a  mature  shell.  The  costas  are  crossed  by  more  or  less  regular  con- 
centric lines  of  growth  of  varying  strength  which  become  more  crowded 
towards  the  outer  margin. 


68  MISSISSIPPIAN    HUACIIIOl'ODA 

Remarks.-  This  species  has  been  established  upon  two  specimens,  one 
pedicle  .iikI  one  brachial  valve.  Hot li  are  from  the  Burlington  limestone 
of  Henderson  County.  Illinois,  and  were  apparently  found  in  association, 
although  they  are  not  the  opposite  valves  of  a  single  specimen.  Both 
valves  arc  imperfect  in  several  particulars,  although  their  outlines  are 
well  shown,  and  the  brachial  valve  has  been  considerably  -crushed.  In 
neither  specimen  are  the  internal  characters  shown  except  very  im- 
perfectly, so  it  cannot  be  stated  with  absolute  certainty  that  no  median 
septum  is  present-  in  the  pedicle  valve,  but  the  shell  is  exfoliated  and  par- 
tially removed  in  the  umbonal  region  of  the  specimen  and  there  seems  to 
be  no  such  structure  present.  In  this  specimen  the  muscular  scar  is 
partially  exposed;  il  seems  to  be  large  and  flabellate,  reaching  beyond 
the  middle  of  the  valve.  The  marginal  convexity  of  the  pedicle  valve, 
which  has  been  described,  is  doubtless  due  to  old  age  of  the  specimen, 
and  in  younger  examples  the  surface  would  doubtless  be  concave  from 
the  beak  to  the  front  margin.  The  species  is  somewhat  similar  to  the 
one  which  has  been  here  described  as  S.  chouteauensis,  but  it  is  very  much 
larger  besides  having  its  greatest  width  along  the  hinge-line,  having 
subauriculate  cardinal  extremities. 

Horizon. — Burlington  limestone. 

Genus  STREPTORHYNCHUS  King 

Description. — Shell  biconvex,  usually  subglobose  in  form,  the  pedicle 
valve  or  both  valves  more  or  less  distorted  and  irregular  in  manner 
of  growth,  the  hinge-line  shorter  than  the  greatest  width  of  the  shell. 
Cardinal  area  of  the  pedicle  valve  variable  in  height,  differentiated  into 
a  primary  and  a  secondary  area  as  in  Schucliertella,  the  delthyrium  closed 
to  its  apex  with  the  deltidium.  Internally  the  pedicle  valve  is  nonseptate, 
the  dental  lamella?  are  reduced  to  ridges  which  are  merely  thickenings  of 
the  inner  surface  of  the  cardinal  area  at  the  sides  of  the  delthyrium,  the 
condition  being  essentially  as  in  Schucliertella;  in  the  brachial  valve  the 
cardinal  process  is  elongate  and  deeply  grooved,  its  length  being  depend- 
ant upon  the  convexity  of  the  umbonal  region  of  the  pedicle  valve. 

Remarks. — The  genus  Streptorliynchus,  as  interpreted  by  Hall  and 
Clarke,1  Girty,2  and  Thomas,3  based  upon  S.  pelargonatus  Schl.,  as  the 
genotype,  is  characterized  as  follows :  1,  the  general  form  of  the  shell  ; 
2,  the  absence  of  true  dental  lamellae ;  3,  the  absence  of  a  median  septum 
in  the  pedicle  valve ;  4,  the  elongate,  deeply  grooved  cardinal  process. 
From  Orthotetes  the  genus    differs    conspicuously  in  the  absence  of  the 

1  Pal.  N.  Y.,  vol.  8,  pt.  1,  p.  267  (1894). 

2  The  Gaudalupian  Fauna,  p.  175  (1908). 

3  Mem.  Geol.  Surv.  Gt.  Brit.,  vol.  1,  pt.  2,  p.  89  (1910). 


STREPTORHYNCHUS  69 

median  septum  of  the  pedicle  valve,  from  Schellwienella  it  may  be  distin- 
guished at  once  by  its  biconvex  shell  and  its  irregular  manner  of  growth, 
its  closest  relationship  being  with  Schuchertella.  In  both  Streptorhynchus 
and  Schuchertella  the  median  septum  of  the  pedicle  valve  is  absent,  as  are 
also  true  dental  lamella?,  leaving  then  only  the  greater  convexity  of  the 
valves,  their  irregular  manner  of  growth,  the  shorter  hinge-line  and  the 
form  of  the  cardinal  process  as  diagnostic  characters  of  Streptorhynchus. 
The  distortion  of  the  valves  in  Streptorhynchus,  especially  the  pedicle 
valve,  is  due  to  the  attachment  of  the  shell  by  the  apex  of  that  valve,  while 
Schuchertella  is  unattached. 

Streptorhynchus  tenuicostatum  n.  sp. 
Plate  IV,  Figs.  3-5 

Description. — Shell  of  medium  size  or  a  little  larger,  wider  than  long, 
the  greatest  width  near  the  mid-length  of  the  shell,  subelliptical  in  out- 
line, the  hinge-line  shorter  than  the  greatest  width,  the  cardinal  extrem- 
ities rounded.  The  dimensions  of  a  nearly  complete  but  somewiiat 
crushed  example  are :  length  of  pedicle  valve  28  mm.,  length  of  brachial 
valve  24.5  mm.,  greatest  width  30.6  mm.,  length  of  hinge-line  23  mm., 
thickness  ±10  mm.,  height  of  cardinal  area  3.5  mm.  The  dimensions  of  a 
nearly  perfect  brachial  valve  are :  length  27  mm.,  greatest  width  39.5 
mm.,  length  of  hinge-line  27  mm.,  convexity  6  mm. 

Pedicle  valve  convex,  more  or  less  distorted,  depressed  convex  in  the 
umbonal  region  with  an  irregular  contour  towards  the  lateral  and 
anterior  margins ;  mesial  sinus  obsolete ;  beak  small,  only  slightly  ex- 
tended beyond  the  cardinal  margin ;  cardinal  area  flat,  of  moderate 
height,  sloping  posteriorly  from  the  hinge-line  at  an  angle  of  40  degrees 
or  more,  the  delthyrium  about  as  wide  as  high,  covered  by  a  convex 
deltidium.     Internal  characters  not  observed. 

Brachial  valve  much  more  regularly  convex  than  the  pedicle,  the  great- 
est convexity  near  or  posterior  to  the  middle,  the  surface  more  or  less 
compressed  towards  the  cardinal  extremities,  the  umbonal  region  not 
protuberant  beyond  the  cardinal  margin ;  mesial  portion  of  the  valve  not 
differentiated.  Surface  of  both  valves  marked  by  radiating  costae  but 
those  of  the  two  valves  somewhat  different  in  character.  The  cost*  of  the 
pedicle  valve  are  very  slender  and  angular,  separated  by  broad,  flat,  in- 
tercostal furrows,  from  one  to  three  costae  occupy  the  space  of  one  milli- 
meter, the  new  ones  being  added  by  intercalation  at  intervals  at  the  middle 
of  the  intercostal  furrows ;  the  costas  are  crossed  by  exceedingly  fine, 
somewhat  wavy,  concentric  markings  which  are  more  conspicuous  across 
the  flat  intercostal  furrows;  the  valve  also  marked  by  strong,  irregular, 
wrinkle-like,  concentric  markings.  On  the  brachial  valve  the  radiating 
costae  appear  somewhat  coarser  because  the  intercostal  furrows  more 
nearly  equal  the  costae  in  width,  although  essentially  the  same  number 


70  MISSISSHTIAN    BRACHIOPODA 

occni),v  llic  space  of  one  millimeter,  these  eostie  increase  by  both  bifurca- 
tion ami  intercalation  and  are  crossed  by  concentric  markings  similar  to 
those  of  the  opposite  valve  but  considerably  fainter. 

h'i  marks.  —  This  species  most  resembles  the  specimens  of  8.  ruginosa  from 
the  Salem  and  St.  Louis  limestone,  both  forms  being  characterized  by  the 
short  hinge-line  and  by  the  strong,  irregular,  concentric  wrinkles  of  the 
pedicle  valve,  but  the  brachial  valve  is  much  more  regular  in  contour  in 
this  species  than  in  the  S.  ruginosa.  The  species  under  discussion  may  be 
easily  distinguished  from  8.  ruginosa  by  the  slender  costas  of  the  pedicle 
valve  with  the  broad  intercostal  furrows  and  by  the  character  of  the  fine 
concentric  markings,  also  by  the  difference  in  character  of  the  radiating 
COStse  of  the  tWO  valves. 

Horizon. — Chouteau  limestone. 

Streptoriiynchus  minutum   (Cumings) 
Plate  VI,  Figs.  16-21 

1856.     Orthis  umbraculum  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  12. 

1888.     Streptorhynchus  (Orthis)  Umbraculum  Hall,  12th  Rep.  Geol.  Surv. 

Ind.,  p.  325. 
1901.     Orthothetes  minutus  Cumings,  Am.  Geol.,  vol.  27,  p.  147,  pi.  15, 

figs.  1-16. 
1906.     Orthothetes  minutus  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1297, 
pi.  18,  figs.  1-16.     (Not  pi.  20,  fig.  7). 

Description. — Shell  very  small,  more  or  less  distorted,  wider  than  long, 
subelliptical  to  subquadrate  in  outline,  the  hinge-line  a  little  shorter 
than  the  greatest  width,  the  cardinal  extremities  angular.  The  dimensions 
of  a  small,  complete  specimen  are:  length  of  pedicle  valve  2.1  mm.,  length 
of  brachial  valve  2  mm.,  greatest  width  3.1  mm.,  length  of  hinge-line  2.9 
mm.,  height  of  cardinal  area  .9  mm.  The  dimensions  of  a  larger  pedicle 
valve  are:  length  5.8  mm.,  greatest  width  8.5  mm.,  length  of  hinge-line 
7  mm.,  height  of  cardinal  area  1.8  mm. 

Pedicle  valve  usually  convex  in  young  examples,  becoming  concave 
towards  the  front  margin  with  the  continued  growth  of  the  shell,  the 
surface  most  prominent  at  the  apex  of  the  valve,  from  which  point  it 
slopes  in  nearly  straight,  gently  concave  or  gently  convex  lines  anteriorly 
and  laterally,  always  becoming  concave  towards  the  front  in  adult  speci- 
mens ;  mesial  sinus  obsolete ;  beak  obtusely  pointed,  usually  nearly  erect, 
sometimes  a  little  recurved  or  slightly  incurved ;  cardinal  area  of  moderate 
height,  usually  nearly  flat  but  sometimes  a  little  concave  or  convex,  the 
lateral  margins  usually  sharply  defined,  sometimes  rounding  into  the 
lateral  slopes  of  the  valve ;  the  delthyrium  triangular,  about  as  wide  as 
high,  covered  by  a  convex  deltidium.  Internally  the  cardinal  teeth  are 
widely  divergent,  the  dental  plates  are  restricted  to  slight  ridge-like 
thickenings  of  the  inner  surface  of  the  cardinal  area  on  each  side  of  the 
delthyrium,  the  muscular  scars  are  ill-defined  and  inconspicuous. 


STREPTORHYNCHUS  71 

Brachial  valve  convex,  most  prominent  in  the  umbonal  region  near  the 
hinge-line,  the  surface  more  or  less  compressed  towards  the  cardinal 
extremities,  the  mesial  portion  of  the  valve  sometimes  slightly  flattened 
or  a  little  depressed ;  the  beak  inconspicuous,  very  slightly  or  not  at  all 
produced  beyond  the  hinge-margin.  Internally  there  is  a  broad  and  rather 
low  cardinal  process  which  is  flanked  on  either  side  by  a  widely  diverging 
socket-plate,  from  the  outer  surface  of  which  the  dental  sockets  are  ex- 
cavated. 

Surface  of  both  valves  marked  by  fine,  subangular,  radiating  costge, 
from  three  to  four  in  the  space  of  1  mm.,  which  increase  by  intercalation 
and  by  bifurcation,  crossing  the  costre  are  exceedingly  fine  concentric 
markings  which  sometimes  produce  crenulations  along  the  summits  of 
the  costs?.  Stronger,  concentric  lines  of  growth  are  also  frequently 
present. 

Remarks. — This  little  shell  is  one  of  those  which  exhibits  a  distinct 
tendency  towards  an  irregular  growth  of  the  shell.  As  it  occurs  in  its 
typical  form  the  specimens  have  some  of  the  characteristics  of  immature 
shells,  as  if  they  might  be  the  young  of  a  larger  form.  Beede  has  identified 
as  the  same  species  certain  much  larger  shells  from  the  fauna  of  the 
Salem  limestone,  some  of  which  attain  a  width  of  50  mm.  or  more.  These 
larger  examples  are  evidently  identical,  specifically,  with  the  shell  de- 
scribed by  Hall  and  Clarke  as  Derbya  ruginosa,  and  if  these  minute  ex- 
amples are  really  the  young  of  the  larger  ones,  the  name  8.  minutwm  will 
have  to  give  way  to  Hall  and  Clarke's  prior  name.  However,  it  does  not 
seem  to  have  been  demonstrated  as  yet  that  the  smaller  forms  are  the 
young  of  the  larger,  for  they  do  not  commonly  occur  in  actual  associa- 
tion, and  for  the  time  being  both  names  will  be  retained.  The  largest 
observed  examples  which  are  certainly  referable  to  this  species  do  not 
exceed  5  or  6  mm.  in  length. 

Horizon. — Salem  limestone. 

Streptorhynchus  ruginosum   (Hall  and  Clarke) 
Plate  V,  Figs.  1-19 

1892.     Derbya  ruginosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  p.  346, 

pi.  11A,  figs.  25-27. 
1897.     Derbya  ruginosa  Hall,  14th  Ann.  Rep.  N.  Y.  State  Geol.,  p.  345,  pi. 

5,  figs.  12-14. 
1897.     Streptorhynchus  wittiamsi  Weller,  Trans.  N.  Y.  Acad.  Sci.,  vol.  16, 

p.  255,  pi.  18,  figs.  1-3. 
1906.     Orthothetes  minutus  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,   p. 

1297,  pi.  20,  fig.  7,  (not  pi.  18,  figs.  1-16). 

Description.  —  Shell  of  medium  size  or  larger,  transversely  subelliptical  in 
outline,  the  thickness  sometimes  nearly  equaling  the  length,  both  valves 
unsymmetrically  distorted  and  marked  by  strong,  irregular,  concentric 


72  MISSISSIPPIAN   BRACUIOPODA 

wrinkles;  the  hinge-line  shorter  than  the  greatest  width  of  the  shell,  the 
cardinal  extremities  obtusely  angular,  the  greatest  width  near  the  mid- 
length  of  the  shell.  The  dimensions  of  the  holotype  are:  Length  of  pedicle 
valve  36  mm.,  length  of  brachial  valve  ;S3.8  mm.,  greatest  width  45  mm., 
thickness  31.2  nun..  Length  of  hinge-line  32.5  nun.,  height  of  cardinal  area 
±8  mm. 

Pedicle  valve  moderately  deep,  the  surface  flattened  in  the  umbonal 
region,  somewhal  compressed  towards  the  cardinal  extremities,  irregularly 
depressed  or  concave  towards  the  lateral  and  anterior  margins;  mesial 
sinus  obsolete;  beak  not  prominent,  probably  Lmt  little  or  not  at  all  ele- 
vated above  the  umbonal  surface;  cardinal  area  of  moderate  height,  slop- 
ing a  little  posterior^  from  the  cardinal  line  to  the  apex,  its  lateral  mar- 
gins sloping  in  nearly  straighl  lines  from  the  beak  to  the  cardinal  extrem- 
ities, sharply  defined  in  the  perfect  shell;  the  delthyrium  triangular, 
higher  than  wide.  Internally  the  fiabellate  muscular  scar  reaches  ante- 
riorly to  near  the  middle  of  the  valve,  a  median  septum  is  wanting  and  the 
dental  plates  are  reduced  to  low  ridges  at  the  sides  of  the  delthyrium. 

Brachial  valve  strongly  convex,  much  deeper  than  the  pedicle,  its  great- 
est convexity  a  little  posterior  to  the  middle,  moderately  compressed 
towards  the  cardinal  extremities,  the  umbo  somewhat  protuberant  beyond 
the  cardinal  line ;  the  beak  incurved ;  mesial  sinus  obsolete.  Internally 
the  cardinal  process  is  apparently  of  moderate  size  and  fills  the  lower 
part  of  the  delthyrium  of  the  opposite  valve,  and  the  muscular  seal's 
occupy  a  subovate  region  a  little  less  than  one-third  the  length  of  the 
valve. 

Surface  of  both  valves  marked  by  fine  radiating  costa2,  from  three  to 
four  of  which  occupy  the  space  of  one  millimeter  at  the  front  of  the  type 
specimen,  upon  the  partially  exfoliated  portions  the  positions  of  the  costae 
are  indicated  by  lines  of  papillae.  The  presence  or  absence  of  fine  con- 
centric markings  is  not  indicated  upon  the  type  specimen,  but  both  valves 
are  marked  by  strong  and  irregular,  wrinkle-like  concentric  markings 
which  give  to  the  entire  shell  a  much  distorted  and  irregular  appearance. 

Remarks.— This  species  was  established  by  Hall  and  Clarke  upon  a  single 
internal  cast  from  a  chert  formation,  to  which  some  fragments  of  the  shell 
substance  adhere,  and  it  is  from  this  specimen  that  the  above  description 
has  been  chiefly  made.  It  was  originally  described  as  a  species  of  Derby  a, 
although  the  presence  of  a  median  septum  in  the  pedicle  valve  is  not 
clearly  shown  as  might  be  expected  in  such  an  internal  cast.  At  one 
point,  near  the  center  of  the  flabellate  muscular  scar  a  slight  median 
ridge  is  suggested,  but  nothing  which  can  be  compared  with  the  strong 
median  septum  of  other  species  which  have  been  referred  to  the  genus 
Derbya.  The  type  specimen  is  said  to  have  come  from  the  "Keokuk 
limestone,  New  Providence,  Indiana,"  but  the  lithologic  character  of  the 


STREPTORHYNCHUS  73 

specimen  is  not  similar  to  the  strongly  ferruginous  casts  of  shells  which 
commonly  come  from  1hat  locality,  and  the  specimen  has  rather  the  lith- 
ologic  character  of  some  of  the  St.  Louis  limestone  cherts.  Furthermore, 
in  the  collections  examined,  the  species  has  been  detected  most  commonly 
in  the  typical  St.  Louis  limestone.  These  St.  Louis  limestone  specimens 
agree  well  with  the  holotype  of  the  species  in  the  general  form  of  the 
shell,  in  the  size  of  the  costs',  and  in  the  extraordinary  irregularity  or  dis- 
tortion of  the  shell,  but  in  no  two  examples  are  the  irregularities  of  the 
shell  form  alike.  In  some  specimens  the  umbonal  region  is  much  flat- 
tened, as  in  the  type,  while  in  others  it  is  elevated  and  terminated  by  a 
pointed  and  more  or  less  distorted  beak.  The  convexity  of  the  brachial 
valve  is  also  a  variable  feature.  An  occasional  example  is  found  hav- 
ing a  minimum  amount  of  irregularity  of  shell  growth.  On  grinding 
down  the  beak  of  several  limestone  examples,  no  median  septum  has  been 
detected,  which  confirms  the  observation  made  upon  the  type  specimen. 
The  most  important  specific  characters  of  the  shell  seems  to  be  its  irregu- 
larity of  growth,  although  the  proportional  length  of  the  hinge-line  is 
rather  constant,  as  well  as  the  general  outline  of  the  shell. 
Horizon.— Salem  limestone,  St.  Louis  limestone  and  Batesville  sandstone. 

Streptorhynchus  ULRicHi  Hall  and  Clarke 
Plate  II,  Figs.  17-18 

1892.     Streptorhynchus  Ulrichi  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

p.  351,  pi.  11B,  fig.  15. 
1897.     Streptorhynchus  Ulrichi  Hall,  14th  Ann.  Rep.  N.  Y.  State  Geol., 

p.  350,  pi.  6,  fig.  3. 

Description. — Shell  below  medium  size,  longer  than  wide,  growing  un- 
symmetrically  and  distorted,  marked  by  strong,  irregular,  concentric 
lines  of  growth ;  the  hinge-line  shorter  than  the  greatest  width  of  the 
shell,  the  cardinal  extremities  angular,  the  greatest  width  anterior  to  the 
middle  of  the  shell.  The  dimensions  of  the  holotype,  a  pedicle  valve, 
are :  length  from  front  margin  to  beak  22  mm.,  length  from  front  margin 
to  hinge-line  15  mm.,  greatest  width  20  mm.,  length  of  hinge-line  16  mm., 
depth  6  mm. 

Pedicle  valve  subtrihedral  in  general  form,  the  surface  somewhat  flat- 
tened medially  from  the  beak  towards  the  front,  but  without  a  distinct 
sinus,  sloping  rather  abruptly  towards  the  postero-lateral  margins  and 
sometimes  a  little  compressed  near  the  cardinal  extremities,  becoming  de- 
pressed towards  the  anterior  margin  in  the  holotype ;  beak  prominent, 
distorted  and  produced  posteriorly  far  beyond  the  hinge-line ;  cardinal 
area  high,  concave  and  somewhat  distorted,  the  lateral  margins  sharply 
defined ;  delthyrium  higher  than  wide,  closed  by  a  convex  deltidium.  In- 
ternally the  hinge-teeth  are  supported  by  dental  lamella?  which  are  pro- 


74 


Mississippi  \n  i'i;  \riii(H'(ii)\ 


(luccd  anteriorly  as  Low  ridges  along  the  posterior  half  of   the  muscular 

so;ir;  mi  median  septum;  muscular  scar  ovate,  extended  anteriorly  to  be- 
yond the  mid-length  of  the  valve ;  the  anterior  margin  erenulate  internally. 
Surface  marked  by  numerous  fine,  but  rather  sharp,  radiating  costas  which 
increase  by  implantation,  anteriorly  the  costae  are  subequal,  but  towards 
the  beak  there  is  a  series  of  stronger  ones  with  from  one  to  three  finer 
ones  between.  The  costae  are  crossed  by  strong,  irregular,  concentric 
lines  of  growth,  varying  in  strength  in  different  parts  of  the  valve. 

Brachial  valve  not  known. 

Remarks.  This  species  is  known  only  from  a  single  specimen,  the  holo- 
type,  which  is  a  silicified  pedicle  valve  wholly  free  from  matrix,  both  ex- 
ternally and  internally,  the  valve  is  a  little  incomplete  on  the  margin  and 
lias  lost  the  terminal  portion  of  the  beak.  From  a  single  example,  in  this 
group  of  shells,  the  really  essential  specific  characters  can  hardly  be 
pointed  out,  and  the  above  description  is  therefore  the  description  of  an 
individual  rather  than  of  the  species.  The  characters  most  likely  to  be 
constant  and  of  specific  value  are  the  relative  proportions  of  length  and 
breadth  and  the  length  of  the  hinge-line.  Other  examples,  when  found, 
will  doubtless  vary  in  the  details  of  outline  and  in  the  surface  markings, 
especially  in  the  concentric  markings  of  the  shell. 

Horizon.— Chester  group. 

Genus  ORTHOTETES  Fischer  de  Waldheim 

Description. — Shell  subplano-convex  to  biconvex,  either  regular  or  more 
or  less  distorted  in  manner  of  growth.  The  pedicle  valve  flat  or  convex, 
the  cardinal  area  rather  high  and  sloping  posteriorly  from  the  hinge-line, 
divided  into  a' primary  and  secondary  area  as  in  Schuchertella  and  other 
allied  genera,  the  delthyrium  closed  to  the  apex  by  the  deltidium.  In- 
ternally the  dental  lamella?  are  produced  anteriorly  towards  the  inner 
floor  of  the  valve  and  are  joined  to  a  median  septum  which  sometimes 
reaches  nearly  half  the  length  of  the  valve.  Towards  the  apex  of  the 
beak  is  a  small,  triangular,  pyramidal  cavity  or  chamber  formed  by  the 
two  dental  lamella;  internally  and  the  inner  surface  of  the  deltidium  ex- 
ternally. The  brachial  valve  convex,  with  a  very  narrow  cardinal  area 
or  with  the  cardinal  area  wanting. 

Remarks.— The  septate  shells  here  included  in  the  genus  Orthotetes  were 
referred  to  Derbya  first  by  Waagen1  and  later  by  Hall  and  Clarke,2  the 
name  Orthothetes  being  used  by  these  authors  for  a  large  group  of  non- 
septate  shells.     It  has  been  shown  by  Girty,3  however,  that  the  original 


lMem.  Geol.  Surv.  India,  ser.  13,  vol.  1,  p.  591  (1887). 

2  Pal.  N.  Y.,  vol.  8,  pt.  1,  p.  261  (1892). 

3  The  Guadalupian  Fauna,  pp.  186-199  (1908). 


OBTHOTETES  75 

specimens  of  Orthotetes  described  and  illustrated  by  Fischer  de  Waldheim 
were  examples  of  a  septate  shell  essentially  identical  as  to  generic  char- 
acters with  Waagen's  and  Hall  and  Clarke's  interpretation  of  Derbya. 
For  the  accommodation  of  the  nonseptate  shells  called  Orthotetes  by  these 
authors.  Girty  has  proposed  the  name  Schuchertella,  which  genus  has  al- 
ready been  discussed  in  this  report.  Among  the  septate  shells  two  rather 
distinct  types  are  recognized,  in  one  of  which,  the  true  Orthotetes,  the 
septa  are  joined  to  form  a  small  triangularly  pyramidal  cavity  in  the  ros- 
tral portion  of  the  pedicle  valve,  while  in  the  other  group,  for  which  the 
name  Derbya  is  retained,  no  such  rostral  cavity  is  present.  In  the  Mis- 
sissippian  faunas  here  considered  only  two  species  of  these  septate  shells 
are  recognized,  in  both  of  which  the  rostral  cavity  is  commonly  present, 
although  it  is  often  small  and  sometimes  the  union  of  the  dental  lamella? 
with  the  septum  is  more  or  less  incomplete. 

Orthotetes  keokuk  (Hall) 
Plate  VII,  Figs.  1-4 

1849.     Orthis  crenistria  Yandall  and  Shumard,  Cont.  to  Geol.  Ky.,  pp.  19, 

21. 
1858.     Orthis  keokuk  Hall,  Geol.  Iowa,  vol.  1.  pt,  2,  p.  640,  pi.  19,  figs.  5a-b. 
1883.     StreptorhyncJius  keokuk  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi. 

(11)  41,  figs.  1-3. 
1890.     Orthis  keokuk  Gordon,  Am.  Geol.,  vol.  5,  p.  261,  pi.  1,  fig.  7. 
1892.     Derbya  Keokuk  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  11, 

figs.  1-3. 
1894.     Orthis  keokuk  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  63. 
1899.     Derbya  keokuk  Girty,  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p.  524. 

Description.  —  Shell  large,  transversely  subelliptical  in  outline,  the 
greatest  width  near  the  mid-length  of  the  shell,  the  hinge-line  shorter 
than  the  greatest  width,  the  cardinal  extremities  rounded  or  obtusely  an- 
gular. The  dimensions  of  a  nearly  complete  but  somewhat  undersized 
specimen  are :  length  of  pedicle  valve  64  mm.,  length  of  brachial  valve  60 
mm.,  greatest  width  -4-80  mm.,  length  of  hinge-line  ±65  mm.,  height  of 
cardinal  area  8.7  mm.,  thickness  of  shell  25.6  mm. 

Pedicle  valve  nearly  flat,  usually  slightly  concave  in  the  central  portion 
and  a  little  elevated  in  the  umbonal  region  towards  the  beak ;  mesial  sinus 
obsolete ;  cardinal  area  flat,  of  moderate  height,  sloping  posteriorly  from 
the  hinge-line  to  the  apex  at  an  angle  of  about  128  degrees  to  the  plane  of 
the  valve,  the  lateral  margins  sharply  defined  and  angular ;  the  delthy- 
rium  about  as  wide  or  a  little  wider  than  high,  completely  closed  by  a 
convex  deltidium.  .  Internally  a  strong  median  septum  extends  from  the 
beak  anteriorly  for  about  one-third  the  length  of  the  valve;  the  teeth  are 
supported  by  short,  non-septate  dental  plates  which  are  scarcely  more 
than  thickened  ridges  upon  the  inner  surface  of  the  shell,  one  on  each  side 


76  MISSISSIPPIAN    BRACHIOPODA 

of  the  delthyrium,  the  dental  plates  usually  join  the  median  septum  near 
the  beak  to  form  a  shallow,  triangular  chamber  in  ihe  apex  of  the  valve; 
the  muscular  impression  is  large  and  flabellate,  triangularly  subovate  in 
outline,  qo1  deeply  impressed,  and  reaching  nearly  or  quite  to  the  middle 
of  the  valve. 

Brachial  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  more  abruptly  to  the  cardinal  margin  and 
less  abruptly  to  the  lateral  and  a  id  erior  margins,  distinctly  compressed 
towards  the  cardinal  extremities,  the  umbo  projecting  slightly  posteriorly 
beyond  the  hinge-line;  median  sinus  obsolete,  although  the  median  por- 
tion of  the  valve  is  frequently  if  not  always  slightly  flattened.  Internally 
the  cardinal  process  is  strong,  extending  conspicuously  beyond  the  car- 
dinal margin,  it  is  slightly  bifid  at  the  extremity  and  is  produced  ante- 
riorly as  a  distinct,  flattened,  ridge-like  thickening  upon  the  inner  surface 
of  the  valve,  which  at  first  contracts  in  width  from  the  base  of  the  car- 
dinal process  and  then  expands  anteriorly  as  it  is  gradually  merged  with 
the  general  inner  surface  within  the  umbonal  region  of  the  valve;  at  the 
base  of  the  cardinal  process  the  hinge  sockets  are  excavated  in  the  sides 
of  that  process,  the  socket  or  crural  plates  being  insignificant  in  their 
development;  muscular  scars  ill-defined,  often  scarcely  distinguishable. 

Surface  of  both  valves  marked  by  fine,  subangular,  radiating  costa^ 
which  are  somewhat  irregular  in  size  and  increase  by  bifurcation  and  in- 
tercalation, from  1  to  3  occupying  the  space  of  one  millimeter.  When 
the  surface  is  uninjured  the  costse  are  crossed  by  exceedingly  fine,  con- 
centric strise,  and  by  occasional,  distinct,  concentric,  wrinkle-like  lines  of 
growth.  Upon  the  internal  surface  of  the  shell,  as  shown  in  internal 
casts,  concentric  markings  nearly  equaling  the  radiating  costas  in  size,  but 
somewhat  more  weakly  developed,  are  commonly  noticeable,  which  give 
to  the  surface  a  distinctly  reticulate  appearance. 

Remarks. — It  has  been  shown  by  Girty1  that  the  typical  species  of  the 
genus  Orthotetes  Fischer  de  Waldheim,  possesses  a  median  septum  in  the 
pedicle  valve,  which  is  the  essential  character  of  the  genus  Derbya  as  de- 
fined by  Waagen,  a  condition  which  necessitates  the  abandonment  of  the 
name  Derbya  and  the  substitution  of  a  new  generic  name  for  the  shells  to 
which  Hall  and  Clarke  have  applied  the  name  Orthotetes.  There  are 
recognized  among  the  septate  shells  of  Waagen 's  genus  Derbya,  two  rather 
distinct  groups  of  species,  in  one  of  which  the  septate  dental  plates  join 
with  the  median  septum  and,  with  the  delthyrium,  enclose  a  triangular 
chamber  in  the  apical  portion  of  the  pedicle  valve,  while  in  the  second 
group  of  species  no  such  triangular  chamber  is  present.  It  happens  that 
the  genotype  of  Orthotetes  is  a  member  of  the  first  or  camerate  division 
of  the  genus,  while  that  of  Derbya  is  one  of  the  simply  septate  forms,  so 

1U.  S.  Geol.  Survey,  Prof.  Paper,  No.  58,  pp.  186-199  (1908). 


ORTIIOTETES  77 

that  if  it  be  considered  advisable  to  retain  the  two  groups  as  of  generic 
value  the  name  Orthotetcs  would  be  applicable  to  one  and  Derbya  to  the 
other.  This  procedure  seems  to  be  unwarranted,  however,  for  the  reason 
that  the  species  under  consideration,  O.  keokuk,  is  essentially  intermedi- 
ate in  character  between  the  two  types.  In  it,  the  dental  plates  cannot  be 
said  to  be  septate,  but  near  the  apex  of  the  valve  they  usually  do  join  the 
median  septum  in  such  a  manner  as  to  inclose  a  short  triangular  chamber, 
but  not  a  deep  one  extending  from  the  apex  to  or  nearly  to  the  hinge-line, 
as  in  the  case  of  the  more  typical  representatives  of  the  camerate  division. 
In  some  examples  of  0.  keokuk  the  triangular  chamber  may  be  scarcely 
distinguishable  at  all,  and  in  one  specimen  observed  the  dental  plate  is 
joined  Avith  the  median  septum  on  one  side  but  not  on  the  other. 

This  species  is  the  largest  representative  of  this  type  of  shell  in  our 
Mississippian  faunas,  and  sometimes  attains  a  width  of  100  millimeters. 

Horizon.— Keokuk  limestone. 

Orthotetes  kaskaskiensis  (McChesney) 
Plate  VI,  Figs.  1-14,  15? 

1860.     Orthis  kaskaskiensis  McChesney,  Desc.  New  Pal.  Foss.,  p.  31. 
1892.     Derbya  kaskaskiensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi. 
1TB,  fig.  6. 

Description. — Shell  above  medium  size,  subelliptical  or  subcircular  in 
outline,  often  somewhat  distorted,  broader  than  long,  the  greatest  width 
near  the  mid-length  of  the  shell,  the  hinge-line  shorter  than  the  greatest 
width,  the  cardinal  extremities  rounded  or  obtusely  angular.  The  dimen- 
sions of  two  nearly  perfect  specimens  are  :  length  of  pedicle  valve  41  mm. 
and  28.3  mm.,  length  of  brachial  valve  37.7  mm.  and  25.2  mm.,  greatest 
width  49.5  mm.  and  34.8  mm.,  length  of  hinge-line  35.5  mm.  and  28.5  mm., 
height  of  cardinal  area  9  mm.  and  5.6  mm.,  thickness  from  deepest  part 
of  brachial  valve  to  apex  of  pedicle  valve  19.5  mm.  and  14  mm. 

Pedicle  valve  nearly  flat  or  somewhat  concave  except  in  the  umbonal 
region  where  the  beak  is  frequently  rather  abruptly  elevated,  sharply 
pointed  and  more  or  less  distorted ;  mesial  sinus  obsolete ;  cardinal  area 
Dearly  flat,  sometimes  a  little  concave  or  convex  towards  the  apex,  sloping 
posteriorly  from  the  hinge-line  at  an  angle  of  from  100  to  140  degrees, 
most  commonly  about  120  degrees,  the  lateral  margins  well  defined  and 
sharply  angular,  sloping  from  the  apex  of  the  beak  to  the  cardinal  ex- 
tremities in  nearly  a  straight  line  or  with  a  slight  concavity  near  the 
beak  and  a  slight  convexity  near  the  cardinal  extremities ;  delthyrium 
much  higher  than  wide,  closed  by  a  rather  strongly  convex  deltidium 
which  is  usually  longitudinally  flattened  or  slightly  sinuate.  Internally 
a  strong  median  septum  originates  at  the  beak  and  extends  anteriorly, 
the  dental  plates  are  short,  nonseptate,  being  scarcely  more  than  thick- 


18  MlssissilM'l.W    BRACHIOPODA 

ened  ridges  on  the  interior  of  the  shell,  one  at  each  margin  of  the  delthy- 
rium,  near  the  apes  of  1 1) «•  beak  the  dental  plates  arc  sometimes  slightly 
extended  anteriorly  and  join  with  the  median  septum  to  form  a  shallow, 
t  riangular  chamber. 

Brachial  valve  convex  throughout  except  towards  the  cardinal  ex- 
tremities, which  arc  compressed,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  more  abruptly  to  the  cardinal  margins,  the 
umbonal  region  not  protuberant  beyond  the  cardinal  margin;  mesial 
portion  of  the  valve  not  differentiated.      Internal  characters  not  observed. 

Surface  of  both  valves  marked  by  abruptly  elevated,  radiating  costae 
which  commonly  alternate  in  size,  and  which  increase  by  bifurcation  and 
implantation.  From  two  to  three  costce  occupy  the  space  of  1  mm.,  the 
intercostal  spaces  usually  being  a  little  broader  than  the  costae.  The 
costa'  are  crossed  by  more  or  less  wrinkle-like,  concentric  lines  of  growth 
which  are  variously  distributed,  usually  being  somewhat  more  crowded 
towards  the  margin  of  mature  shells,  and  by  very  fine  raised  concentric 
lines  which  are  best  developed  in  the  intercostal  spaces  and  which  give 
to  the  surface,  with  the  costas,  a  finely  reticulate  appearance  when  they 
are  best  developed. 

B<  marks — This  species  differs  from  0.  keokuk  in  its  smaller  size,  its  less 
protuberant  umbonal  region  in  the  brachial  valve,  and  usually  in  the  more 
abruptly  elevated  and  more  acute  beak  of  the  pedicle  valve.  The  relation 
of  the  dental  plates  to  the  median  septum  is  similar  to  that  in  0.  keokuk, 
these  species  being  somewhat  intermediate  in  condition  between  the 
camerate  and  septate  divisions  of  the  genus.  Hall  and  Clarke  illustrate 
an  internal  view  of  an  example  which  shows  a  shallow  triangular  cham- 
ber in  the  beak  of  the  pedicle  valve,  but  other  specimens  which  have 
been  examined  indicate  that  no  junction  of  the  dental  plates  with  the 
septum  exists,  and  consequently  no  triangular  chamber. 

Horizon. — Ste.  Genevieve  limestone  and  Chester  group. 

Family  PRODUCTION 

Genus  CHONETES  Fischer  de  Waldheim 

Description. — Shell  usually  small,  concavo-convex,  subsemicircular  in 
outline,  broader  than  long,  the  greatest  width  along  the  hingedine.  Pedicle 
valve  convex,  usually  flattened  towards  the  cardinal  extremities,  with  a 
narrow  cardinal  area ;  the  delthyrium  closed  to  the  apex  by  the  deltidium ; 
the  lateral  margins  of  the  area  sharply  defined,  bearing  a  single  row  of 
hollow,  vertical  or  divergent  spines  which  increase  in  length  towards  the 
cardinal  extremities ;  internally  the  muscular  scars  are  usually  faint,  the 
surface  outside  the  scars  is  strongly  papillose,  the  papillae  appearing  in 
internal  casts  as  pits.  Brachial  valve  concave,  with  a  cardinal  area  much 
narrower  than  that  of  the  opposite  valve,  and  without  marginal  spines; 


CHONETES  79 

internal  surface  papillose  as  in  the  opposite  valve.  External  surface  of 
both  valves  marked  by  usually  fine,  radiating  eostrc,  sometimes  concen- 
trically marked  also,  rarely  nearly  smooth. 

Remarks. — This  easily  recognized  genus  is  represented  by  numerous 
species  and  an  abundance  of  individuals  in  the  lower  Mississippian  faunas, 
but  after  the  close  of  the  Osage  epoch  it  becomes  exceedingly  rare.  The 
spines  of  the  cardinal  margin,  which  are  so  characteristic  of  the  genus 
are  rarely  well  preserved,  but  their  bases  commonly  can  be  detected 
upon  most  fairly  preserved  specimens. 

Chonetes  multicosta  Winchell 
Plate  VIII,  Figs.  8-16 

1863.  Chonetes  multicosta  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  5. 

1869.  Chonetes  multicosta  Winchell,  Safford's  Geol.  Tenn.,  p.  443. 

1870.  Chonetes  multicosta  Winchell,  Proc.  Am.  Phil.  Soc,  vol.  11,  p.  250. 
1909.  Chonetes  illinoisensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  297, 

pi.  12,  fig.  11. 

Description. — Shell  concavo-convex,  length  two-thirds,  or  a  little  less,  of 
the  width,  the  greatest  width  usually  at  the  hinge-line  but  in  some  speci- 
mens the  hinge-line  is  a  little  shorter  than  the  greatest  width,  the  cardinal 
extremities  usually  nearly  rectangular,  the  lateral  margins  straight  or 
slightly  convex  posteriorly,  becoming  regularly  convex  anteriorly  and 
passing  with  unbroken  curvature  into  the  anterior  margin  which  becomes 
gently  convex  or  nearly  straight  in  its  median  portion.  The  dimensions 
of  Winchell's  type  specimen,  a  pedicle  valve,  are:  length  13  mm.,  width 
20.5  mm.,  convexity  3.5  mm. 

Pedicle  valve  depressed-convex,  the  greatest  convexity  posterior  to  the 
middle,  compressed  towards  the  cardinal  extremities,  the  surface  flattened 
along  the  mesial  region  and  usually  slightly  depressed  in  a  rather  broad, 
shallow,  ill-defined  mesial  sinus  in  the  anterior  two-thirds  of  the  shell; 
beak  small,  very  slightly  produced  beyond  the  cardinal  margin ;  cardinal 
area  narrow,  slightly  concave,  lying  at  an  angle  of  about  140  degrees  to 
the  plane  of  the  valve,  its  lateral  margins  sharply  defined  and  bearing 
about  five  oblique  spines  on  each  side  of  the  beak ;  the  delthyrium  broadly 
triangular,  much  wider  than  high.  The  inner  surface  of  the  valve  finely 
papillose  beyond  the  middle,  the  papilla?  appearing  as  small  pits  upon 
the  surface  of  internal  casts  of  the  valve. 

Brachial  valve  only  moderately  concave,  somewhat  flattened  towards 
the  cardinal  extremities.  The  cardinal  area  not  well  shown  on  any  of 
the  examples  examined,  but  it  is  probably  small.  The  internal  characters 
not  observed. 

Surface  of  both  valves  marked  throughout  by  fine,  usually  regular, 
radiating  costa?,  which  increase  by  bifurcation  on  the  pedicle  valve  and 


s"  MISSISSIITIAN    BRACHIOPODA 

by  intercalation  on  the  brachial  valve,  from  200  to  235  are  present  at 
the  distal  margin  of  full  grown  shells,  from  17  to  20  occupying  the  space 
of  three  millimeters ;  near  the  beak  and  towards  the  cardinal  extremities 
they  become  SOmewhal  liner  than  in  the  middle  part  of  the  front  of 
t  be  shell. 

Remarks.-  The  specimens  indicated  as  the  types  of  this  species  in  the 
'  niversity  of  Michigan  collection  are  eight  in  number,  their  horizon  and 
locality  being  marked  "Chemung  Group,  Burlington,  la."  The  so-called 
Chemung  Group  at  Burlington,  of  Winchell's  time,  is  now  included  in 
the  Kinderhook,  and  to  one  familial-  with  the  Burlington  section  the 
several  specimens  may  be  recognized  from  their  lithologie  characters  as 
having  come  from  more  than  one  horizon  in  the  Kinderhook,  and  perhaps 
even  from  the  base  of  the  Burlington  limestone.  At  least  four  of  the 
specimens  are  clearly  from  bed  No.  7,  the  topmost  bed  of  the  Kinderhook 
at  Burlington,  two  examples,  which  may  be  specifically  distinct,  are  from 
the  Chonopectus  sandstone;  one  is  from  a  white,  granular  chert  which 
may  he  from  the  Kinderhook  oolite  bed,  but  is  more  probably  from  the 
Burlington  limestone ;  and  the  last  specimen  is  from  the  brownish, 
crystalline  limestone  which  is  so  characteristic  of  the  lower  Burling- 
ton. The  measurements  given  by  Winchell  in  his  original  definition 
of  the  species,  agree  with  those  of  the  last  specimen  mentioned  above 
from  the  Lower  Burlington  limestone,  and  as  this  is  in  many  respects 
the  most  perfect  individual  of  the  lot  it  is  believed  to  be  the  one  from 
which  the  greater  part  of  the  original  definition  was  written. 

The  species  has  been  commonly  confused  with  C.  illinoisensis,  but  a 
careful  study  of  the  original  specimens  seems  to  establish  the  species  as 
a  good  one.  It  grows  to  a  larger  size  than  C.  illinoisensis  and  has  more 
angular  cardinal  extremities,  the  greater  width  of  the  shell  usually 
being  along  the  hinge-line,  while  in  C.  illinoisensis  the  hinge-line  is  dis- 
tinctly shorter  than  the  greatest  width  and  the  cardinal  extremities  are 
rounded.  The  radiating  costs  are  also  often  somewhat  finer  than  in 
C.  illinoisensis,  although  this  distinction  is  not  always  to  be  depended 
upon,  since  the  more  finely  marked  examples  of  C.  illi7ioisensis  are  essen- 
tially identical  in  this  character  with  the  more  coarsely  marked  specimens 
of  C.  multicosta;  on  the  average,  however,  the  costae  of  mxdticosta  are 
slightly  finer  than  those  of  illinoisensis.  In  no  specimen  examined  have 
the  cardinal  spines  been  well  preserved,  and  even  the  spine  bases  are 
commonly  very  obscure,  but  there  are  clearly  more  than  two  or  three, 
as  indicated  by  Winchell,  and  there  is  apparently  no  basis  for  the  state- 
ment of  that  author  that  they  extend  at  nearly  right  angles  to  the  hinge- 
line. 

Horizon. — Upper  Kinderhook  and  Burlington  limestone. 


CHONETES  81 

Chonetes  illinoisensis  Worthen 
Plate  VIII,  Figs.  63-70 

1858.     Chonetes  logani  Hall,  Geol.  Iowa.  vol.  1.  pt.  2,  p.  598,  pi.  12,  figs. 

la-e,  2.     (Not  C.  logani  N.  &  P.,  1855.) 
1860.     Chonetes  Illinoiensis  Worthen,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1, 

p.  571. 
1863.     Chonetes  Illinoiensis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  5. 
1865.     Chonetes  Illinoisensis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  116. 
1868.     Chonetes  Illinoisensis  Meek  and  Worthen,  Geol.  Surv.  111.,  vol.  3, 

p.  505,  pi.  15,  figs.  8a-b. 
J 870.     Chonetes  Illinoisensis  Winchell,   Proc.   Amer.   Phil.   Soc,   vol.   11, 

p.  251. 
1888.     Chonetes  illinoisensis  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3, 

p.  35,  pi.  3,  fig.  21. 
1890.     Chonetes  illinoisensis  Herrick,  Bull.  Geol.  Soc.  Amer.,  vol.  2,  p.  48, 

pi.  1,  fig.  16. 
1894.     Chonetes  illinoisensis  Keyes,  Mo.  Geol.  Survey,  vol.  5,  p.  53. 
1903.     Chonetes  illinoisensis  Girty,  U.  S.  Geol.  Survey,  Prof.  Paper  No.  16, 

p.  279. 

Description. — Shell  concavo-convex,  the  length  about  two-thirds  the 
width,  the  hinge-line  usually  a  little  shorter  than  the  maximum  width, 
the  hinge  extremities  a  little  rounded  or  nearly  rectangular,  lateral  mar- 
gins slightly  convex  or  nearly  straight,  more  strongly  curved  anteriorly 
and  passing  with  a  regular  curvature  into  the  anterior  margin,  which 
becomes  nearly  straight  for  a  short  distance  in  the  middle  portion.  The 
dimensions  of  a  specimen  of  about  average  size  are :  length  11.9  mm., 
width  16.3  mm.,  convexity  3.6  mm. 

Pedicle  valve  depressed  convex,  the  greatest  convexity  posterior  to  the 
middle,  compressed  towards  the  cardinal  extremities,  flattened  along  the 
mesial  region  and  sometimes  depressed  in  a  shalloAV,  ill-defined  mesial 
sinus ;  the  beak  small,  scarcely  extended  beyond  the  cardinal  margin ; 
cardinal  area  narrow,  slightly  concave,  lying  at  an  angle  of  about  145 
degrees  to  the  plane  of  the  valve,  its  lateral  margins  sharply  defined  and 
bearing  five  or  six  oblique  spines  upon  each  side ;  the  delthyrium  broadly 
triangular,  about  twice  as  wide  as  high,  the  deltidium  small,  confined 
to  the  apex  and  margins  of  the  delthyrium. 

Brachial  valve  only  slightly  concave,  a  little  flattened  towards  the  car- 
dinal margins ;  the  cardinal  area  not  well  shown  on  any  of  the  authentic 
specimens,  but  it  is  probably  small.  Internally  the  cardinal  process  is  of 
moderate  size,  and  from  its  anterior  side  a  pair  of  ridges  of  variable 
strength  diverge  widely,  becoming  nearly  parallel  with  the  cardinal  mar- 
gin and  extending  nearly  half  way  to  the  cardinal  extremities;  a  second 
pair  of  ridges  originate  in  front  of  the  cardinal  process,  border  the  basal 
portion  of  the  muscular  scar,  diverging  with  an  angle  of  about  50  degrees, 


82  MISSISSIPPIAN  BBACHIOPODA 

between  them  a  median  ridge  develops  and  continues  anteriorly  some- 
times reaching  the  middle  of  the  valve;  towards  the  anterior  border  and 
extending  to  the  Lateral  borders,  the  inner  surface  of  the  valve  is  papil- 
lose, the  papilla'  being  arranged  more  or  less  regularly  in  radiating  lines, 
and  the  inner  border  of  the  valve  is  costate,  the  costa)  corresponding  with 
i  hose  of  I  lie  external  surface. 

The  surface  of  both  valves  is  marked  throughout  by  fine,  nearly  regu- 
lar, radiating  costse,  which  increase  by  bifurcation  on  the  pedicle  valve 
and  by  intercalation  upon  the  brachial  valve.  The  total  number  of  costce 
varies  from  175  fo  225,  according  to  the  size  of  the  individual,  but  the  size 
of  the  costffi  is  nearly  constant,  about  six  occupying  the  space  of  one 
millimeter,  except  near  the  beak,  where  they  are  somewhat  finer. 

Remarks. — The  typical  horizon  for  this  species  is  the  Burlington  lime- 
stone, where  it  sometimes  occurs  in  great  numbers.  Ordinarily  the  aver- 
age size  of  the  species  is  about  15  mm.  or  a  little  more  in  width. 

In  Worthen's  original  desciiption  of  the  species  the  number  of  costa? 
are  said  to  be  100  to  120  or  more,  but  this  number  is  understated,  as  has 
been  determined  from  the  examination  of  authentic  examples  from  the 
typical  locality.  In  Meek  and  Worthen's  description  of  the  species  12 
to  14  costa1  are  said  to  be  present  in  .10  inch,  which  would  be  nearly  the 
number  observed  on  specimens  studied  by  the  writer,  6  costas  in  1  mm. 
would  be  equivalent  to  15  in  .10  inch.  Winchell's  C.  multicosta  is  a 
closely  allied  species,  but  grows  to  a  larger  size ;  it  also  has  a  longer  hinge- 
line  and  more  angular,  cardinal  extremities  than  C.  illinoisensis,  and 
usually  has  somewhat  finer  costa?.  C.  shumardiana  DeKoninck,  with 
which  C.  illinoisensis  has  sometimes  been  confused,  is  an  entirely  different 
species,  and  a  comparison  of  the  two  forms  is  made  under  the  description 
of  that  species. 

Horizon. — Burlington  limestone,  Keokuk  limestone. 

Chonetes  missouriensis  n.  sp. 
Plate  VIII,  Fig.  20 

Description. — Shell  transversely  subelliptical  in  outline,  the  hinge-line 
a  little  shorter  than  the  greatest  width  of  the  shell,  the  cardinal  extremi- 
ties obtusely  angular  or  a  little  rounded.  The  lateral  margins  gently  con- 
vex posteriorly,  curving  more  rapidly  towards  the  front  and  passing 
without  interruption  into  the  anterior  margin  which  is  gently  convex  in 
the  middle.  The  dimensions  of  the  holotype  are :  length  16.7  mm.,  width 
26  mm.,  convexity  5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  beak  and  gently  to  the  cardinal  margin,  becoming  com- 
pressed towards  the  cardinal  extremities ;  the  median  portion  of  the  valve 
flattened  or  slightly  depressed  in  a  broad,   shallow,  ill-defined  median 


C1I0NETES  83 

sinus;  the  umbo  a  little  prominent  and  projecting  slightly  beyond  the 
cardinal  margin;  the  beak  small  and  incurved;  the  cardinal  margin 
sharply  defined  and  bearing  about  four  spines  on  each  side  of  the  beak; 
cardinal  area  not  observed. 

Brachial  valve  only  moderately  concave,  flattened  towards  the  cardinal 
extremities,  the  greatest  concavity  posterior  to  the  middle.  Internally 
the  cardinal  process  is  small  and  is  flanked  by  a  pair  of  widely  divergent 
ridges  which  become  nearly  parallel  with  the  cardinal  margin  and  reach 
about  one-third  the  distance  to  the  cardinal  extremities,  and  in  whose  pos- 
terior side  the  dental  sockets  are  excavated  ;  in  front  of  the  socket  ridges  a 
well-defined  median  septal  ridge  reaches  to  about  the  middle  of  the  valve, 
and  also  a  pair  of  ridges,  one  on  each  side  of  the  median  ridge,  which 
originate  at  the  base  of  the  median  ridge,  with  a  slight  divergence,  and 
curve  towards  the  lateral  margins,  distally  attaining  a  length  of  about 
two-thirds  that  of  the  median  ridge. 

Both  valves  marked  by  fine,  rounded,  radiating  costa>,  separated  by 
narrower  intercostal  furrows,  the  costas  increase  by  division  on  the  ped- 
icle valve  and  by  intercalation  on  the  brachial  valve,  from  3  to  4  occupy 
the  space  if  1  millimeter,  about  170  being  present  altogether  upon  the 
specimen  whose  dimensions  have  been  given.  Crossing  the  costae  are 
several  irregularly  distributed  lines  of  growth  of  variable  strength. 

Remarks.  —  This  species  is  most  nearly  allied  to  C.  illinoisensis  but  it 
attains  a  larger  size  and  has  a  much  coarser  costae,  there  being  only  3 
or  4  in  the  space  of  1  millimeter,  while  in  C.  illinoisensis  there  are  6  in 
the  same  space. 

Horizon.— Pierson  limestone  of  the  Kinderhook. 

Chonetes  chesterensis  n.  sp. 
Plate  VIII,  Figs.  31-34 

Description. — Shell  concavo-convex,  the  length  about  two-thirds  the 
width,  the  greatest  width  along  the  hinge-line,  the  cardinal  extremities 
angular;  lateral  margins  nearly  straight  or  slightly  concave  in  front  of 
the  cardinal  extremities,  convexly  curved  anteriorly  and  passing  with 
unbroken  curvature  into  the  anterior  margin  which  becomes  nearly 
straight  in  its  central  portion.  The  dimensions  of  two  specimens  are : 
length  of  pedicle  valve  8.2  mm.  and  8.7  mm.,  length  of  brachial  valve 
7.1  mm.  and  7.8  mm.,  greatest  width  12.6  mm.  and  12.5  mm.,  convexity 
2  mm.  and  2.5  mm. 

Pedicle  valve  depressed-convex,  the  greatest  convexity  near  the  middle, 
the  surface  curvature  a  little  more  abrupt  to  the  anterior  margin  than 
towards  the  beak,  compressed  towards  the  cardinal  extremities;  beak 
small,  scarcely  produced  beyond  the  cardinal  margin;  cardinal  area  low, 
nearly  flat  except  towards  the  apex  where  it  is  slightly  concave,  lying 


84  MISSISSIPPIAN   BRACHIOPODA 

;it  jin  angle  of  aboul  130  degrees  to  the  plane  of  the  valve,  its  lateral  mar- 
gins sharply  defined  and  bearing  six  oblique  spines  upon  each  side  of  the 
beak;  deltbyrium  broadly  triangular,  the  deltidium  confined  to  the  apex 
and  the  lateral  margins.     Interna]  characters  not  observed. 

Brachial  valve  gently  concave  posteriorly,  becoming  more  strongly 
curved  towards  the  anterior  and  lateral  margins;  cardinal  area  about 
one-half  the  height  of  thai  of  the  opposite  valve,  with  which  its  surface 
makes  a  very  broad  angle,  being  nearly  180  degrees.  The  cardinal  pro- 
cess filling  the  greater  portion  of  the  deltbyrium  of  the  other  valve,  the 
remaining  internal  characters  not  observed. 

Surface  of  both  valves  marked  by  fine,  regular,  radiating  costas  which 
increase  by  bifurcation  and  intercalation,  from  100  to  120,  are  present 
aboul  tin'  margin  of  an  average  specimen,  about  five  or  sometimes  six 
occupying  the  space  of  one  millimeter,  except  towards  the  cardinal  ex- 
tremities where  they  become  finer  and  more  or  less  obscure,  they  are  also 
somewhat   finer  towards  the  beaks  of  the  valves. 

Remarks.— This  species  has  its  nearest  allies  in  C.  Illinois ensis  and  C. 
viul ticosla.  It  differs  from  both  these  species  in  its  smaller  size,  and 
from  C.  illinoisensis  if  differs  in  its  proportionately  more  elongate  hinge- 
line,  the  greatest  width  of  the  shell  being  at  the  hinge-line.  The  propor- 
tional length  of  the  hinge-line  is  similar  to  that  of  C.  multicosta  but  be- 
sides being  a  much  smaller  species  it  possesses  somewhat  coarser  costae. 
The  species  is  the  only  one  as  yet  observed  in  the  Chester  faunas,  where 
it  is  one  of  the  rarer  forms. 

Horizon.— Chester  group,  Paint  Creek  formation. 

Chonetes  logani  Norwood  and  Pratten 
Plate  VIII,  Figs.  43-46 

1855.     Chonetes  Logani  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci.  Phil. 

(2),  vol.  3,  p.  30,  pi.  2,  figs.  12a-c. 
1865.     Chonetes  Logani  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  116. 
1867.     Chonetes  logani  Hall,  Pal.  N.  Y.,  vol.  4,  pi.  22,  figs.  23,  26-27. 
1888.     Chonetes  logani  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3,  p.  35, 

pi.  7,  fig.  22,  pi.  3,  fig.  12. 
1888.     Chonetes  logani  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3,  p.  35, 

pi.  7,  fig.  22;  pi.  3,  fig.  12. 
1892.     Chonetes  Logani  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  16, 

fig.  25. 
1894.     Chonetes  logani  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  53. 
1901.     Chonetes  logani  Weller,  Trans.  St.  Louis  Acad.  Sei.,  vol.  11,  p.  182, 

pi.  16,  figs.  10-11. 
1909.     Chonetes  logani  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  299,  pi.  12, 

figs.  12-13. 

Description.— Shell  strongly  convex,  subsemielliptical  in  outline,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  acutely  an- 


CHONETES  85 

gular  or  sometimes  approaching  rectangular,  the  auricular  portion  small 
and  not  sharply  differentiated  from  the  body  of  the  shell,  the  lateral  mar- 
gins nearly  straight  or  slightly  concave  posteriorly,  convex  anteriorly 
and  passing  without  break  into  the  regularly  rounded  anterior  margin, 
the  length  usually  a  little  less  than  two-thirds  the  width.  The  dimensions 
of  three  specimens  are :  length  6.3  mm.,  6.8  mm.,  10.5  mm. ;  width  8.9  mm., 
9.5  mm.,  13.5  mm. ;  convexity  2.6  mm.,  3.5  mm.,  5.8  mm. 

Pedicle  valve  most  convex  near  or  a  little  posterior  to  the  middle,  the 
surface  curving  abruptly  to  the  beak  and  a  little  more  gently  to  the  ante- 
rior margin,  compressed  towards  the  cardinal  extremities  but  with  the 
auriculations  small,  not  sharply  differentiated,  and  convex  from  the  car- 
dinal margin  posteriorly ;  mesial  sinus  obsolete ;  the  beak  small,  produced 
slightly  beyond  the  cardinal  margin,  the  umbonal  surface  smooth  for  a 
short  distance  from  the  beak;  the  cardinal  area  narrow,  slightly  concave, 
extending  posteriorly  in  nearly  the  plane  of  the  valve,  the  delthyrium 
small,  the  cardinal  margin  sharply  defined,  bearing  tAvo  or  three  spines  on 
each  side  of  the  beak,  all  of  which  are  directed  obliquely  outward.  In- 
ternally the  muscular  scars  are  rather  strongly  defined,  and  are  divided 
along  the  median  line  of  the  valve  by  a  median  septum  which  varies  in 
strength  in  different  individuals  from  a  slightly  raised  line  to  a  strongly 
raised,  narrow  ridge ;  beyond  the  limits  of  the  muscular  scars  the  surface 
is  papillose  throughout. 

Brachial  valve  deeply  concave,  the  greatest  concavity  near  the  middle, 
becoming  flatter  and  only  gently  concave  in  the  auricular  regions  towards 
the  cardinal  extremities ;  the  cardinal  area  narrower  than  that  of  the  op- 
posite valve  and  meeting  it  in  an  obtuse  angle ;  the  costaB  do  not  extend  to 
the  beak  but  leave  a  small,  smooth  area  at  the  apex  of  the  valve  in  the 
middle  of  which,  adjacent  to  the  cardinal  margin,  a  small,  node-like  prom- 
inence is  sometimes  present. 

Surface  of  both  valves  marked  by  rather  broad,  depressed,  rounded 
costaB  much  broader  than  the  intervening  furrows,  about  three  of  which 
occupy  the  space  of  one  millimeter,  on  the  pedicle  valve  they  increase  by 
division  and  on  the  brachial  valve  by  implantation ;  crossing  the  cost* 
are  exceedingly  fine,  raised  concentric  lines,  10  or  more  in  the  space  of 
one  millimeter,  which  are  obsolete  in  the  furrows  between  the  costas,  and 
give  to  the  costas  a  distinctly  crenulate  appearance ;  the  costaB  do  not 
originate  at  the  beak,  but  at  a  little  distance  to  the  front,  and  they  become 
faint  or  sometimes  obsolete  towards  the  cardinal  extremities. 

Remarks.— This  species  is  a  common  member  of  the  fauna  of  the  Kinder- 
hook  oolite  bed  at  Burlington,  Iowa,  where  it  is  associated  with  the  less 
common  C.  burlingtonensis,  from  which  it  differs  in  its  greater  convexity, 
its  greater  proportional  length,  its  broader  and  less  numerous  costaB,  and 
the  transverse  crenulations  of  the  costaB.     In  the  transverse  markings  of 


8fi  \i  ississii'i'l.W    BRACHIOPODA 

the  costse  the  species  resembles  ('.  ornatus  of  the  Louisiana  limestone,  but 
the  shell  is  more  strongly  convex  with  less  well  developed  auriculations 
and  with  less  elevated  cost  as. 
Horizon.     Kinderhook. 

(  Ihonetbs  ornatus  Shumard 

Plate  VIII,  Pigs.  21-29 

1855.     Chonetes  ornata  Shumard,  Geol.  Rep.  l\Io.,  p.  202,  pi.  C,  tigs.  la-c. 
1894.     Chom  tes  ornata  ITeyes,  Mo.  Geol.  Survey,  vol.  5,  p.  53,  pi.  38,  fig.  2, 
1899.     Chonetes  ornatus  Girty,  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p.  527, 

pi.  68,  figs.  4a-d. 
L908.     ('limn  its  tinnitus  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 

ser.,  p.  75,  pi.  17,  figs.*20-2:5. 

Description.  —  Shell  subsemielliptical  in  outline,  wider  than  long,  the 
Length  a  little  more  than  two-thirds  the  width,  the  greatest  width  usually 
along  the  hinge-line,  the  cardinal  extremities  angular,  the  lateral  margins 
a  Little  sinuate  or  nearly  straight  in  the  posterior  half,  passing  with  a 
regular  curvature  into  the  anterior  margin  in  front.  The  dimensions  of 
two  examples  are:  length  6.9  mm.  and  7.5  mm.,  width  10  mm  and  11.5  mm., 
convexity  2.7  mm.  and  3  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  near  or  a  little 
posterior  to  the  middle,  compressed  towards  the  cardinal  extremities  with 
a  rounded  ill-defined  sinus  passing  from  each  side  of  the  beak  obliquely 
to  the  lateral  margins,  the  auriculations  formed  by  these  oblique  sin- 
uses are  convex  in  an  antero-posterior  direction ;  mesial  sinus  obsolete  or 
represented  by  a  slight  mesial  flattening  of  the  valve;  beak  small,  com- 
pressed, scarcely  extending  beyond  the  cardinal  margin ;  cardinal  area 
narrow,  nearly  flat,  extending  posteriorly  in  nearly  the  plane  of  the 
valve;  the  delthyrium  small,  about  as  wide  as  high,  about  one-half  of  its 
area,  the  apical  portion,  covered  by  a  convex  deltidium  with  a  sinuate 
cardinal  margin ;  the  cardinal  margin  sharply  defined,  sloping  from  each 
side  of  the  beak  to  the  cardinal  extremities  and  bearing  one,  two,  or  three 
spines  upon  each  side. 

Brachial  valve  rather  deeply  concave  in  the  middle,  flattened  and  auric- 
ulate  towards  the  cardinal  extremities,  the  auriculations  being  concave  in 
an  anterior-posterior  direction ;  cardinal  area  with  a  sharply  defined 
margin,  much  narrower  than  that  of  the  opposite  valve,  the  areas  of  the 
two  valves  meeting  in  an  obtuse  angle ;  at  the  center,  opposite  the  delthy- 
rium of  the  opposite  valve,  a  prominent,  convex  chilidium  surrounds  the 
posterior  surface  of  the  cardinal  process. 

Surface  of  each  valve  marked  by  from  thirty  to  thirty-eight  rounded 
costae,  none  of  which  occupy  the  auricular  portions,  from  two  and  one- 
half  to  three  occupying  the  space  of  one  millimeter;  those  of  the  pedicle 
valve  increase  by  bifurcation  and  those  of  the  brachial  valve  by  implan- 


CHONETES  87 

tation.  In  addition  to  the  cost*  each  valve  is  ornamented  by  exceedingly 
6ne  concentric  markings,  stronger  on  the  pedicle  than  on  the  brachial 
valve,  which  are  obsolete  in  the  furrows  between  the  costae,  and  by 
stronger  concentric  lines  of  growth  which  sometimes  become  lamellose. 

Remarks.  —  This  species  has  sometimes  been  confused  with  the  form  here 
referred  to  C.  glenparkensis,  indeed  Shumard,  the  author  of  the  species, 
probably  included  in  it  specimens  which  are  really  C.  glenparkensis,  as  he 
mentions  a  Chouteau  limestone  locality,  Cooper  County,  Missouri,  as  one 
of  his  type  localities.  Among  recent  collections  the  species  has  been  ob- 
served only  in  the  fauna  of  the  Louisiana  limestone,  all  the  Chouteau  lime- 
stone examples  with  similar  markings  being  C.  glenparkensis.  The  species 
differs  from  C.  logani  in  its  somewhat  larger  size,  its  more  conspicuous 
a  uric ulations,  its  stronger  and  somewhat  coarser  costae.  It  resembles 
C.  logani  in  its  fine  concentric  markings  which  are  conspicuous  upon  the 
tops  of  the  costa;  and  become  obsolete  in  the  intervening  furrows. 

Horizon. — Louisiana  limestone. 

Chonetes  glenparkensis  Weller 

Plate  VIII,  Figs.  30,  47-49 

1906.     Chonetes  glenparkensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1.6, 
p.  441,  pi.  6,  fig.  7. 

Description.  —  Shell  subsemielliptical  in  outline,  the  length  about  two- 
thirds  the  width,  the  greatest  width  along  the  hinge-line,  the  cardinal  ex- 
tremities acutely  angular  and  sometimes  a  little  acuminate.  Lateral 
margins  nearly  straight  or  slightly  concave  posteriorly,  their  directions 
converging  anteriorly,  towards  the  front  they  round  into  the  regularly 
convex  anterior  margin  without  interruption.  The  dimensions  of  two 
specimens  are:  length  8  mm.  and  7.5  mm.,  width  ±12.5  mm.  and  ±12.4 
mm.,  convexity  2.8  mm.  and  3  mm. 

Pedicle  valve  strongly  convex,  inflated  in  the  central  portion  and  con- 
spicuously compressed  towards  the  cardinal  extremities,  the  auriculations 
convex  from  the  cardinal  margin  anteriorly,  the  greatest  convexity  of  the 
valve  near  the  middle,  the  surface  curving  a  little  more  abruptly  to  the 
beak  than  to  the  anterior  margin ;  mesial  sinus  obsolete ;  the  umbo  rather 
prominent  and  a  little  protuberant  beyond  the  cardinal  margin ;  the 
beak  small  and  incurved ;  cardinal  margin  sharply  defined,  with  three  or 
four  spines  on  each  side  of  the  beak  directed  obliqiiely  outward.  Inter- 
nally the  muscular  scars  are  only  moderately  developed,  being  divided 
along  the  median  line  of  the  shell  by  a  slight  ridge  extending  anteriorly 
from  the  beak ;  beyond  the  region  occupied  by  the  muscular  impressions 
the  surface  is  strongly  papillose,  the  papilla'  being  arranged  in  more  or 
less  regular,  radiating  lines  and  being  obsolete  towards  the  cardinal  ex- 
tremities. 


,KS  aiSSISSIPPIAJS    BBACHIOPCDA 

Brachial  valve  deeply  concave,  the  greatesl  concavity  near  the  middle, 
ihe  concavity  becoming  shallow  in  the  auricular  portions  of  the  valve 
towards  the  cardinal  extremities;  the  cardinal  area,  the  cardinal  process 
and  the  internal  characters  of  1 1 1  *  -  valve  not  observed. 

Surface  of  both  valves  marked  by  rather  <$©arse,  rounded,  radiating 
costse,  separated  by  intercostal  Furrows  about  c*«jum  1  to  ihc  eost;e  in  width, 
and  increasing  by  division  and  intercalation;  from  two  to  three  costae 
occupy  the  space  of  one  millimeter,  about  35  being  present  altogether 
upon  an  average  sized  specimen,  upon  the  auricular  portions  of  the  shell 
lln\  become  faint  or  entirely  obsolete.  Crossing  1  lie  costaj  are  fine, 
raised,  concentric  markings  which  are  strongly  developed  upon  the  tops 
of  the  COStae  and  are  entirely  obsolete  in  the  intercostal  furrows,  giving 
to  the  costse  in  well  preserved  specimens  a  strongly  crenulate  appearance. 

I,' i  murks. — This  species  was  originally  described  from  a  single  indi- 
vidual from  the  Glen  Park  limestone,  which  was  evidently  water-worn 
before  it  was  fossilized.  A  comparison  of  this  specimen  with  numerous 
individuals  from  the  Chouteau  limestone  seems  to  establish  the  identity 
of  the  two  forms.  In  the  Glen  Park  specimen,  a  pedicle  valve,  the  auric- 
ular portions  of  the  shell  have  been  eroded  and  the  cardinal  extremities 
seem  to  be  rounded ;  but  the  size  and  convexity  of  the  valve,  the  costae, 
and  the  nature  of  the  concentric  markings  are  entirely  similar  in  the  Glen 
Park  and  the  Chouteau  limestone  specimens.  The  only  difference  worthy 
of  note  is  the  slightly  coarser  and  consequently  less  numerous  costa3  on 
the  Glen  Park  specimen,  although  some  individuals  or  some  parts  of  indi- 
viduals from  the  Chouteau  limestone  have  fully  as  coarse  costaj  as  does 
the  Glen  Park  specimen.  The  description  here  given  has  been  drawn  up 
primarily  from  the  Chouteau  limestone  specimens. 

The  Chouteau  limestone  specimens  included  in  this  species  were  origin- 
ally included  in  the  species  C.  ornatus  by  Shumard,  and  the  original  illus- 
tration of  that,  species  was  perhaps  taken  from  one  of  this  species.  The 
description  of  C.  ornatus,  however,  seems  to  have  been  chiefly  taken  from 
the  Louisiana  limestone  specimens,  and  the  name  is  here  restricted  to  the 
shells  from  that  formation.  C.  glenparkensis  differs  from  C.  ornatus  in 
the  much  greater  convexity  or  inflation  of  the  pedicle  valve  and  the 
greater  concavity  of  the  brachial  valve,  and  in  the  greater  extension  of 
the  shell  along  its  hinge-line  and  consequently  in  the  more  conspicuous 
auriculations  of  the  shell.  The  ornamentation  of  the  surface,  especially 
the  crenulated  costa?,  is  similar  in  the  two  species,  and  this  character  was 
evidently  considered  as  of  specific  rank  by  Shumard,  but  it  is  now  known 
to  be  common  to  several  species  of  the  genus.  The  species  is  perhaps 
most  closely  allied  to  C.  logani.  and  has  sometimes  been  so  identified,  but 
it  may  be  distinguished  by  its  greater  average  size,  although  some  ex- 
amples of  C.  logani  are  fully  as  large  as  any  example  of  C.  glenparkensis, 


CHONETES  89 

by  the  greater  extension  of  the  hinge-line  and  more  conspicuous  auricu- 
Latious  of  the  shell,  and  by  the  somewhat  coarser  costae  separated  by  pro- 
portionally wider  intercostal  furrows. 

Horizon. — Glen  Park  limestone  and  Chouteau  limestone  of  the  Kinder- 
book. 

Chonetes  shumakdanus  DeKoninck 

Plate  VIII,  Figs.  1-7 

1847.     Chonetes  shumardiana  DeKoninck,  Monog.  du  Gen.  Prod,  et  Chon., 

p.  192,  pi.  20,  figs.  la-d. 
1855.     Chonetes  Shumardiana  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci. 
Phil.,  (2),  vol.  3,  p.  24. 

Description.  —  Shell  semielliptical  in  outline,  the  proportional  length, 
breadth,  and  convexity  variable,  the  greatest  width  along  the  hinge-line, 
the  cardinal  extremities  usually  nearly  rectangular ;  the  lateral  margins 
nearly  straight  posteriorly,  curving  regularly  into  the  anterior  margin 
in  front.  The  dimensions  of  three  nearly  perfect  examples  are :  length 
16  mm.,  12.5  mm.  and  11.5  mm.,  width  22  mm.,  15  mm.  and  17  mm.,  con- 
vexity 6  mm.,  5.5  mm.  and  4.2  mm. 

Pedicle  valve  varying  in  its  convexity,  but  never  extreme  in  either  di- 
rection, the  greatest  convexity  near  or  a  little  back  of  the  middle,  com- 
pressed and  auriculate  towards  the  cardinal  extremities  but  with  the 
auriculations  not  sharply  differentiated  from  the  body  of  the  shell ;  mesial 
sinus  entirely  obsolete ;  the  beak  small  and  inconspicuous,  the  umbo  pro- 
jecting a  little  beyond  the  cardinal  margin ;  cardinal  area  nearly  flat, 
slightly  twisted  towards  the  cardinal  extremities,  lying  in  nearly  the 
plane  of  the  valve;  the  delthyrium  about  as  wide  as  high,  closed  towards 
its  apex  by  a  convex  deltidium,  its  lower  portion  filled  by  the  posterior 
portion  of  the  cardinal  process  of  the  opposite  valve ;  the  cardinal  mar- 
gins sharply  defined,  bearing  the  bases  of  from  3  to  5  oblique  spines.  In- 
ternally the  muscular  scars  are  heart-shaped  in  outline  and  in  the  younger 
individuals  reach  nearly  to  the  middle  of  the  valve,  becoming  proportion- 
ally smaller  with  age,  they  are  well  developed  and  become  rather  deeply 
impressed  in  old  shells,  a  thin  median  septum  is  present  which  extends 
from  the  beak  nearlpto  the  middle  of  the  muscular  scar,  towards  the  car- 
dinal extremities  the  valve  is  thickened  internally,  the  thickened  portion 
more  or  less  sharply  differentiating  a  central,  subovate,  deeply  concave 
region  from  the  more  flattened,  subtriangular  regions  towards  the  car- 
dinal extremities ;  the  inner  surface  of  the  valve,  beyond  the  muscular 
scars,  covered  by  papilhe  which  are  scattered  towards  the  central  portion 
of  the  valve,  becoming  much  more  numerous  and  more  prominent  towards 
the  lateral  and  anterior  margins. 

Brachial  valve  deeply  concave  in  the  central  portion,  with  an  indistinct 
sinus  on  each  side  extending  from  the  center  obliquely  towards  the  car- 


90  MISSISSIPPIAN    BRACHIOPODA 

dinal  extremities;  cardinal  area  much  narrower  than  that  of  the  opposite 
valve  and  sloping  anteriorly  so  as  to  form  a  very  wide  angle  with  it,  each 
side  a  Little  twisted  towards  tin-  cardinal  extremities  and  sloping  gently 
from  the  lateral  extremities  to  the  center  so  that  the  two  sides  are  not  in 

one  plane;  the  <|iiadri-par1  ate  posterior  extremity  of  the  cardinal  proeess 
is  distinctly  visible  at  the  center  of  the  cardinal  area  and  tills  a  portion  of 

the  delthyriiini  of  the  opposite  valve.  Internally  the  cardinal  process  is 
prominent  and  the  muscular  scars  are  large  and  well  defined,  the  inner 
surface,  including  a  portion  of  the  surface  of  the  muscular  scars,  is  cov- 
ered with  papilhc  which  are  arranged  more  or  less  definitely  in  radiating 
rows  towards  the  lateral  and  anterior  margins. 

Surface  of  both  valves  marked  by  line  radiating  cost®,  variable  in 
width,  from  5  to  9  occupying  the  space  of  one  millimeter,  they  increase  by 
bifurcation  upon  the  pedicle  valve  and  by  implantation  on  the  brachial; 
they  are  crossed  by  much  finer,  raised,  concentric  markings  which  are  ob- 
solete in  the  furrows  between  the  costa1,  giving  to  the  costse  a  sort  of  cren- 
ulated  appearance;  when  partially  exfoliated  the  intercostal  furrows  ex- 
hibit a  row  of  fine,  regularly  arranged  pits. 

Remarks.  The  shell  which  is  here  identified  as  Chonetes  shumardanus 
occurs  abundantly  in  the  basal  Knobstone  shales  of  Kinderhook  age, 
among  the  "Knobs,"  south  of  Louisville,  Kentucky.  This  is  the  typical 
locality  for  DeKoninck's  species,  and  although  his  original  description 
and  illustrations  do  not  exactly  fit  the  shells  which  commonly  occur 
there,  the  identification  is  believed  to  be  correct.  The  greatest  discrep- 
ency  between  DeKoninck's  description  and  the  specimens  is  in  the  size  of 
the  costae.  DeKoninck's  statement  that  120  occupy  the  space  of  10  milli- 
meters would  make  12  in  one  millimeter,  which  is  about  twice  as  many  as 
the  average  among  the  specimens  examined.  The  specimens  studied, 
however,  exhibit  much  variation  in  this  character,  the  most  finely  marked 
specimen  having  9  costas  in  1  millimeter.  DeKoninck's  description  also 
indicates  a  less  convex  shell  than  is  usual  among  our  specimens.  It  is  a 
notable  fact  that  among  the  specimens  studied  the  lesser  convexity,  finer 
costa%  and  greater  proportional  breadth,  are  characters  which  are  asso- 
ciated, and  the  writer  has  sometimes  been  tempted  to  refer  these  alone  to 
DeKoninck's  species,  and  to  erect  a  new  species  for  the  narrower,  more 
convex,  and  more  coarsely  marked  forms  which  are  always  by  far  the 
most  numerous.  This  procedure  has  not  been  followed,  however,  because 
both  types  occur  together  with  intermediate  forms,  and  other  characters 
remain  much  more  constant.  The  row  of  minute  pits  in  the  intercostal 
furrows  of  slightly  exfoliated  specimens  is  a  conspicuous  feature  of  all 
the  shells,  and  one  which  is  mentioned  and  illustrated  by  DeKoninck. 
Without  access  to  DeKoninck's  type  specimens,  which  are  not  in  America, 
it  is  not  possible  to  be  absolutely  certain  what  shell  he  had,  or  to  deter- 


CHONETES  91 

mine  whether  his  statement  in  regard  to  the  size  of  the  eostse  is  correct, 
but  these  shells  from  the  "Button  Mould  Knobs"  cannot  be  referred  to 
any  other  described  species,  and  if  they  are  not  C.  shwnardanus  they  must 
belong  to  an  unnamed  form. 

This  shell  has  sometimes  been  confused  with  ('.  illinoisi  nsis,  with  which 
some  specimens  agree  closely  in  form,  size,  and  size  of  costas,  but  they  con- 
stantly differ  from  that  species  by  reason  of  the  transverse  markings  or 
crenulations  of  the  eostse  which  are  entirely  absent  in  C.  illinoisensis. 
As  regards  these  markings  of  the  shell,  C.  shumardanus  resembles  C. 
logani  and  G.  ornatus,  but  it  differs  from  both  these  species  in  other  essen- 
tial characters. 

Horizon. — New  Providence  shale  of  the  Kinderhook,  Kentucky. 

Chonetes  gkegarius  Weller 

Plate  VIII,  Figs.  71-72 

1901.     Chonetes  gregarius  Weller,   Trans.   St.  Louis  Acad.   Sci.,  vol.   11, 
p.  149,  pi.  12,  fig.  2. 

Description. — Shell  small,  usually  subelliptical  in  outline,  the  length 
about  four-fifths  the  width,  hinge-line  usually  a  little  shorter  than  the 
greatest  width  of  the  shell  and  the  cardinal  extremities  a  little  rounded, 
but  in  some  specimens  the  cardinal  extremities  are  rectangular  and  the 
hinge-line  equal  to  the  greatest  width  of  the  shell.  Lateral  margins 
gently  convex  or  sometimes  nearly  straight  posteriorly,  becoming  more 
convex  anteriorly  and  rounding  without  interruption  into  the  anterior 
margin,  which  is  gently  convex  in  it's  median  portion.  The  dimensions 
of  three  specimens  are :  length  4.2  mm.,  5.1  mm.,  and  6.1  mm. ;  width  5.8 
mm.,  6  mm.,  and  8  mm. ;  convexity  1.5  mm.,  1.6  mm.,  and  2  mm. 

Pedicle  valve  most  convex  at  a  point  posterior  to  the  middle,  from 
which  point  the  surface  curves  more  abruptly  to  the  beak  than  to  the 
front  margin,  the  convexity  of  the  valve  often  extends  well  out  towards 
the  cardinal  extremities,  the  amount  of  compression  of  the  valve  in 
that  region  being  variable  but  never  excessive ;  mesial  sinus  obsolete ; 
the  beak  small,  scarcely  extended  beyond  the  cardinal  margin ;  car- 
dinal margin  sharply  defined,  bearing  the  bases  of  about  two  spines 
on  each  side  of  the  beak ;  cardinal  area  narrow,  lying  in  nearly  the  plane 
of  the  valve,  the  delthyrium  of  medium  size,  closed  at  its  apex  by  a 
convex  deltidium.  Internally  a  slight  median  ridge  extends  anteriorly 
from  the  beak,  the  muscular  scars  are  weakly  developed  and  the  sur- 
face is  papillose  towards  the  anterior  and  lateral  margins. 

Brachial  valve  moderately  concave,  the  greatest  concavity  posterior 
to  the  middle,  the  surface  flattened  towards  the  cardinal  extremities ; 


92  MISSISSIPPIAN  BRACHIOPODA 

cardinal  area  narrow,  the  cardinal  process  small.  Internally  the  mus- 
cular scars  arc  of  only  moderate  strength,  and  the  surface  papillae  are 
well  developed. 

Surface  of  both  valves  marked  by  very  fine,  subangular  costal,  which 
increase  by  intercalation  and  by  division,  about  eight  or  more  occupying 
the  space  of  1  millimeter,  from  75  to  100  being  present  upon  each  valve 
depending  upon  the  size  of  the  valve.  Crossing  the  costas  are  minute, 
concentric,  raised  lines,  which  are  undeveloped  in  the  intercostal  furrows, 
and  which  give  to  the  oostffi  when  the  surface  is  perfectly  preserved,  a 
crenulate  appearance. 

Remarks. — In  its  size  and  general  form  this  species  resembles  C. 
in  mculatus,  but  it  differs  conspicuously  from  that  species  in  its  much 
liner  costse,  there  being  twice,  or  more  than  twice,  as  many  in  this 
species  upon  shells  of  equal  size.  The  concentric  markings  of  the  shell 
are  also  different,  they  being  of  the  same  type  as  those  of  C.  logani 
and  C.  ornatus;  the  pedicle  valve  is  less  convex  and  the  brachial  valve 
less  concave  than  in  ('.  n< ■niciilnl its.  The  more  minute  surface  markings 
of  this  species  are  commonly  obliterated  in  the  usual  condition  of  preser- 
vation of  the  shells,  and  only  one  individual  observed  among  a  great 
number  has  satisfactorily  shown  the  concentric  markings  which  appear 
as  crenulations  of  the  costse.  In  no  case  have  the  cardinal  spines  of 
the  species  been  observed  and  upon  the  great  majority  of  specimens 
even  the  spine  bases  cannot  be  detected. 

Horizon. — Kinderhook. 

Chonetes  geniculatus  White 
Plate  VIII,  Figs.  35-42 

1862.  Chonetes  geniculate/,  White,  Proc.  Boston  Soe.  Nat.  Hist.,  vol.  9,  p.  29. 
1894.     Chonetes  geniculatus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  53,  pi.  38, 

fig.  3. 
1908.     Chonetes  geniculatus  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  75,  pi.  17,  figs.  15-19. 

Description. — Shell  small,  subsemielliptical  in  outline,  rather  strongly 
concavo-convex,  the  convexity  extending  well  out  towards  the  cardinal 
extremities,  the  length  about  five-sixths  of  the  width,  the  length  of  the 
hinge-line  equal  to,  or  a  little  shorter  than,  the  greatest  width  of  the 
shell;  the  cardinal  angles  rectangular  or  a  little  obtuse,  lateral  margins 
nearly  straight  or  slightly  convex  posteriorly,  rounding  into  the  anterior 
margin  in  front.  The  dimensions  of  two  specimens  are :  length  5  mm. 
and  5.7  mm.,  width  6  mm.  and  6.9  mm.,  convexity  1.8  mm.  and  2  mm. 

Pedicle  valve  most  convex  near  the  middle,  a  little  compressed  towards 
the  cardinal  extremities,  but  the  auriculations  are  small  and  not  sharply 
differentiated  from   the   body   of  the   shell ;   mesial  sinus   obsolete,   but 


CIIONETES  93 

with  the  median  portion  of  the  valve  sometimes  a  little  flattened;  car- 
dinal area  narrow,  slightly  concave,  lying  in  nearly  the  plane  of  the 
valve,  delthyrinm  small,  closed  towards  the  apex  by  the  convex  deltidium ; 
the  cardinal  margin  sharply  defined,  bearing  about  three  spines  on 
each  side  of  the  beak  which  are  directed  obliquely  outward;  the  beak 
small  and  but  slightly  extended  beyond  the  cardinal  margin,  the  umbo 
inconspicuous. 

The  brachial  valve  moderately  concave  in  the  median  portion,  the 
greatest  concavity  near  the  middle,  becoming  flattened  towards  the  car- 
dinal extremities ;  the  cardinal  area  narrower  than  that  of  the  opposite 
valve  and  meeting  it  in  a  widely  obtuse  angle  or  lying  in  nearly  the 
same  plane ;  the  posterior  extremity  of  the  cardinal  process  tripartite 
and  tilling  the  basal  portion  of  the  delthyrium  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  depressed,  rounded  costa?,  about 
four  or  five  in  the  space  of  one  millimeter,  and  from  35  to  40  upon 
each  valve,  these  costa?  are  commonly  indistinct  posteriorly  and 
are  frequently  nearly  or  quite  obsolete  to  nearly  the  margin  of  the 
valves;  upon  the  brachial  valve  a  small,  longitudinal,  node-like  prom- 
inence is  present  just  in  front  of  the  middle  of  the  cardinal  margin. 
Aside  from  the  costa?  the  surface  is  marked  by  exceedingly  fine  con- 
centric markings  and  by  a  variable  number  of  much  stronger  lines  of 
growth  which  are  sometimes  nearly  equally  distributed,  but  are  more 
often   crowded   towards   the   front. 

Remarks. — This  little  shell  is  similar  in  general  form  to  C.  logani, 
but  it  is  smaller  and  has  more  nearly  obsolete  costa?  which  are  not 
erenulated  as  are  those  of  that  species.  It  is  associated  with  C.  ornatus, 
from  which  it  may  be  easily  distinguished  by  its  smaller  size,  greater 
relative  convexity  and  much  less  sharply  defined  costa?. 

Horizon . — Louisiana  limestone. 

Chonetes  burlingtonensis  Weller 

Plate  VIII,  Figs.  18-19 

1901.     Chonetes  burlingtonensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
p.  184,  pi.  16,  fig.  '9. 

Description. — Shell  semielliptical  in  outline,  the  length  equal  to  two- 
thirds  the  width,  the  greatest  width  along  the  hinge-line,  the  cardinal 
extremities  nearly  rectangular,  the  lateral  margins  nearly  straight  or 
slightly  convex  posteriorly,  becoming  more  strongly  curved  anteriorly 
and  passing  into  the  anterior  margin  which  becomes  more  gently  convex 
in  its  median  portion.  The  dimensions  of  the  type  specimen  are:  length 
9  mm.,  width  13.5  mm.,  convexity  3  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
rather  abruptly  to  the  beak  and  much  more  gently  to  the  anterior  margin, 


!)4  iMississil'l'lAN    BRACHIOPODA 

compressed  towards  the  cardinal  extremities  but  the  auriculations  qoI 
sharply  differentiated  from  the  body  of  the  valve,  in  the  median  portion 
of  the  valve  the  surface  is  somewhat  flattened,  but  is  not  depressed  in  a 
median  sinus;  the  beak  is  small  and  inconspicuous,  the  umbo  smooth 
at  its  apex,  scarcely  extending  beyond  the  cardinal  line;  cardinal  area- 
ami  delthyrium  not  observed,  the  cardinal  margin  sharply  defined,  bear- 
big  two  or  three  spines  on  each  side  of  the  beak. 

Brachial  valve  moderately  or  rather  deeply  concave,  the  greatest  con- 
cavity posterior  to  the  middle,  the  surface  flattened  or  only  slightly 
concave  towards  the  cardinal  extremities;  the  cardinal  area  very  narrow; 
the  plications  do  qo1  extend  to  the  beak  but  leave  a  small,  smooth  region 
at  the  apex  of  the  valve,  in  the  middle  of  which,  adjacent  to  the  hinge- 
line,  is  a  small,  longitudinal,  sharply  differentiated,  node-like  prom- 
inence. 

Surface  of  both  valves  marked  by  narrow,  sharply  elevated,  rounded 
costse,  which  increase  by  bifurcation  on  the  pedicle  valve  and  by  im- 
plantation on  the  brachial  valve;  they  are  separated  by  narrower  inter- 
costal furrows;  from  three  to  five  costae  occupy  the  space  of  one  milli- 
meter, about  100  being  present  at  the  margin  which  originate  from  the 
bifurcation  of  about  25  initial  ones.  Aside  from  the  costae  the  surface 
is  marked  by  minute,  concentric  lines  which  are  more  strongly  developed 
across  the  intercostal  furrows  than  upon  the  costae  themselves,  and  are 
often  nearly  or  quite  obsolete. 

Remarks. — This  species  resembles  C.  illinoisensis,  but  is  smaller,  with 
coarser  costoa  which  are  separated  by  proportionally  narrower  and 
deeper  intercostal  furrows.  The  concentric  markings  also  differentiate 
the  species  from  C.  illinoisensis,  as  well  as  the  smaller  number  of  cardinal 
spines.  The  species  differs  from  C.  logani,  with  which  it  is  associated, 
in  its  larger  size,  proportionally  less  convexity,  larger  number  of  costae 
and  less  conspicuous  concentric  markings  which  are  not  restricted  to 
the  tops  of  the  costae. 

Horizon. — Kinderhook. 

Chonetes  planumbonus  Meek  and  Worthen 
Plate  VIII,  Figs.  58-62 

1860.     Chonetes  planumbona  Meek  and  Worthen,  Proc.   Acad.  Nat.   Sci. 

Phil.,  p.  450. 
1866.     Chonetes  planumbona  Meek  and  Worthen,  Geol.  Surv.  111.,  vol.  2, 

p.  253,  pi.  18,  figs.  la-d. 

Description. — Shell  concavo-convex,  subsemielliptical  in  outline,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  nearly  rec- 
tangular, the  length  from  two-thirds  to  three-fourths  the  width,  the  lat- 
eral margins  nearly  straight  posteriorly,  becoming  more  convex  towards 


CHONOPECTUS  95 

the  front  and  rounding  regularly  into  the  anterior  margin  which  is  some- 
what straightened  in  its  median  portion.  The  dimensions  of  two  speci- 
mens are:  length  8.9  mm.  and  8.7  mm.,  width  11.9  mm.  and  11.1  mm.,  con- 
vexity 2.8  mm.  and  2.8  mm. 

Pedicle  valve  most  convex  near  or  a  little  in  front  of  the  middle,  the 
surface  commonly  curving  more  abruptly  to  the  anterior  margin  than  to 
the  beak,  slightly  compressed  towards  the  cardinal  extremities  but  onlv 
obscurely  aurieulate ;  mesial  sinus  obsolete,  although  the  mesial  portion 
of  the  valve  is  sometimes  slightly  flattened ;  umbonal  region  somewhat 
flattened,  the  beak  not  produced  beyond  the  cardinal  margin;  the  cardinal 
margin  sharply  defined,  bearing  four  or  five  oblique  spines  on  each  side 
of  the  beak ;  cardinal  area  rather  broad  and  flat,  the  delthyrium  broadly 
triangular  with  a  small  deltidium  closing  its  apical  portion,  the  lateral 
margins  sharply  defined,  bearing  four  or  five,  probably  oblique,  spines  on 
each  side  of  the  beak. 

Brachial  valve  only  moderately  concave,  the  greatest  concavity  in  front 
of  the  middle,  becoming  a  little  flattened  towards  the  cardinal  extremi- 
ties ;  the  cardinal  area  very  narrow.  Internally  the  cardinal  process  is  of 
moderate  size  and  is  flanked  by  a  pair  of  widely  divergent,  rather  short 
ridges,  in  the  outer  sides  of  which  the  dental  sockets  are  excavated ;  the 
muscular  scars  rather  indistinct ;  the  surface  covered  with  elongate  pa- 
pillae which  are  arranged  in  radial  series  and  grow  more  prominent 
towards  the  outer  margins  of  the  valve. 

Surface  of  both  valves  appearing  nearly  smooth  to  the  naked  eye,  but  a 
lens  shows  that  obscure  and  more  or  less  discontinuous  radiating  cost* 
are  present,  and  that  these  are  crossed  by  minute,  raised,  flexuous  and 
discontinuous  concentric  markings. 

Remarks. — This  species  has  only  been  observed  from  the  typical  locality 
in  Monroe  County,  Illinois,  and  in  Ste.  Genevieve  County,  Missouri,  where 
it  sometimes  occurs  in  abundance  in  certain  of  the  limestone  layers.  The 
species  is  easily  recognized  because  of  the  nearly  obsolete  surface  mark- 
ings. The  raised  concentric  markings  of  the  shell  somewhat  resemble 
those  of  C.  logani,  but  they  do  not  have  the  regularity  of  the  similar  mark- 
ings of  that  species,  and  are  more  nearly  continuous  because  of  the  nearly 
obsolete  radiating  costse.  Other  characters  which  distinguish  the  species 
are  the  slight  auriculation  of  the  shell  and  the  anterior  position  of  the 
greatest  convexity  of  the  pedicle  valve. 

Horizon. — Upper  Keokuk  limestone. 

Genus  CHONOPECTUS  Hall  and  Clarke 

Descript ion.  —  Shell  concavo-convex,  broader  than  long,  the  greatest  width 
at  or  near  the  hinge-line ;  cardinal  area  of  the  pedicle  valve  narrow,  its 
lateral  margins  bearing  a  single  row  of  slightly  divergent  spines  which 


96  MISSISSIIM'IAN    BRACHIOPODA 

increase  in  length  towards  the  cardinal  extremities.  The  beak  of  the 
pedicle  valve  is  compressed  and  flattened,  and  sometimes  slightly  dis- 
torted from  attachmenl  in  early  growth.  External  surface  of  both  valves 
marked  by  exceedingly  fine,  radiating  costse,  which  are  crossed  by  a 
double  series  of  oblique  concentric  Lines.  The  concentric  markings  are 
best  developed  on  the  brachial  valve. 

Ki  marks.-  In  its  general  form,  and  in  its  cardinal  spines  this  genus  does 
not  d\l)'vv  essentially  from]  Chonetes,  but  it  can  be  distinguished  at  once 

from  thai  genus  by  means  of  its  surface  markings.  A  single  species  of 
the  genus  is  known  and  the  condition  of  preservation  in  which  it  has  been 
observed  is  not  such  as  to  allow  the  internal  characters  of  the  shell  to  be 
clearly  distinguished,  but  the  inner  surface  of  the  valves  apparently  lack 
the  papilla;  which  are  so  constant  a  feature  in  Chonetes. 

Chonopectus  pischer]  (Norwood  and  Pratten) 
Plate  VIII,  Fig.  73 ;  Plate  LXXXIII,  Figs.  21-22 

1855.     Chonetes  Fischcri  Norwood  and  Pratten,  Join-.  Acad.  Nat.  Sci.  Phil. 

(2),  vol.  3,  p.  25,  pi.  2,  fig.  3. 
1858.     Chonetes  fischcri  Hall,  Geol.  Iowa,  vol.  1,    pt.    2,    p.    517,  pi.  7, 

figs.  la-c. 

1869.  Chonetes  Fischeri  Winchell,  Safford's  Geol.  Tenn.,  p.  443. 

1870.  Chonetes  Fischeri  Winchell,  Proc.  Am.  Phil.  Soc,  vol.  11,  p.  250. 
1883.     Chonetes  Fischcri  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.   (16) 

47,  figs.  17-31. 
"892.     Chonopectus  Fischcri  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt. 

1,  pi.  20,  figs.  24-27. 
1892.     Chonopectus  Fischcri  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi. 

15B,  figs.  20-23 ;  pi.  16,  figs.  17,  31. 

1900.  Chonopectus  fischeri  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  69,  pi.  1,  fig.  17. 

1901.  Chonopectus  fischeri  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11,  pp. 

150,  151,  154,  pi.  12,  fig.  1,  pi.  13,  fig.  17. 

Description.— Shell  concavo-convex,  subelliptical  or  subcircular  in  out- 
line, usually  wider  than  long,  the  hinge-line  usually  a  little  shorter  than 
the  greatest  width  of  the  shell,  the  hinge  extremities  subrectangular  or 
a  little  rounded.  The  lateral  margins  gently  convex  or  nearly  straight 
posteriorly,  curving  more  rapidly  towards  the  front  and  passing  without 
interruption  into  the  broadly  rounded  anterior  margin.  The  dimensions 
of  two  individuals  are:  length  17  mm.  and  21  mm.,  width  24.8  mm.  and 
30.8  mm.,  convexity  of  pedicle  valve  3.5  mm.  and  5  mm. 

Pedicle  valve  most  convex  near  the  middle,  becoming  moderately  com- 
pressed towards  the  cardinal  extremities,  with  no  mesial  sinus  or  mesial 
flattening  of  the  valve ;  the  umbonal  region  usually  a  little  flattened,  the 
beak  scarcely  protuberant  beyond  the  cardinal  margin ;  the  cardinal  mar- 
gin sharply  defined,  bearing  about  four,  slender,  obliquely  curved  spines 


PRODUCTELLA  07 

on  each  side  of  the  beak.  The  cardinal  area,  delthyrium,  and  internal 
characters  of  the  valve  not  observed. 

Brachial  valve  moderately  concave  with  the  greatest  concavity  near  the 
middle  the  surface  becoming  flattened  towards  the  cardinal  extremities; 
al  the  beak  or  initial  point  of  the  valve,  close  to  the  cardinal  margin,  is  a 
small,  round,  node  like  protuberance.  The  cardinal  area,  cardinal  process, 
and  internal  features  of  the  shell  not  observed. 

Surface  of  both  valves  marked  by  tine,  thread-like,  wavy,  discontinu- 
ous, more  or  less  irregular,  radiating  costas,  about  six  of  which  occupy  the 
space  of  one  millimeter,  these  are  crossed  by  still  finer  concentric  striae 
which  give  to  the  uninjured  shell  surface  a  finely  reticulated  ornamenta- 
tion when  examined  under  a  lens.  The  older  half  of  the  shell  is  also  fre- 
quently marked  by  two  sets  of  more  or  less  conspicuous  concentric 
wrinkles  which  cross  each  other  in  the  manner  of  the  engine-turned  mark- 
ings on  a  watch  case.  Irregular  concentric  lines  of  growth  in  the  form  of 
more  or  less  prominent  wrinkles  are  not  infrequently  present. 

//i  murks. — This  species  is  the  only  known  member  of  the  genus,  and  is 
especially  characteristic  of  the  Kinderhook  beds  2,  3  and  4  of  the  Burling- 
ton, Iowa,  section.  The  specimens  sometimes  occur  in  enormous  numbers 
in  the  lower  of  these  beds,  a  yellow  sandstone,  but  it  always  occurs  in  this 
bed  in  the  condition  of  modified  casts  and  moulds  which  do  not  exhibit 
the  true  characters  of  the  surface  markings  to  best  advantage.  These' 
markings  are  better  shown  on  specimens  from  the  limestone  beds  No.  3 
and  4,  except  the  two  sets  of  crossed  concentric  marks  which  usually  are 
more  conspicuous  upon  the  sandstone  specimens,  and  which  seem  to  be 
more  conspicuous  upon  the  brachial  than  upon  the  pedicle  valves. 

The  species  is  exceedingly  variable  in  the  proportional  length  and 
breadth  of  the  shell,  some  specimens  being  considerably  longer  than  wide, 
while  others  are  conspicuously  transverse.  The  specimens  whose  dimen- 
sions have  been  given  are  of  about  average  size  and  form. 

Horizon . — Kinderhook. 

Genus  I'h'ODUCTELLA  Hall 

Description.  —  Shells  below  medium  size,  more  or  less  deeply  concavo- 
convex,  the  hinge-line  straight,  equaling  or  shorter  than  the 
greatest  width  of  the  shell.  Pedicle  valve  convex,  the  beak  more  or  less 
incurved,  dependent  upon  the  amount  of  convexity  of  the  valve ;  a  narrow 
cardinal  area  present,  with  the  delthyrium  closed  by  a  deltidium;  cardinal 
teeth  present.  Brachial  valve  concave,  furnished  with  dental  sockets  and 
socket  plates.  External  surface  of  the  plates  spinose,  the  spines  usually 
arranged  more  or  less  irregularly,  also  marked  by  irregular,  concentric  or 
radiating  marks,  or  by  both. 

—4 


98  MISSISSIPPIAN    BBACHIOPODA 

Remarks.  The  characters  commonly  designated  as  the  essential  fea- 
tures of  Productella  as  distinguished  from  Productus,  viz.,  the  narrow 
cardinal  area  and  weakly  developed  articulating  hinge-teeth  and  sockets, 
can  rarely  be  distinguished  upon  the  specimens,  and  in  actual  practice  the 
type  of  surface  markings  of  the  shell  is  commonly  relied  upon  for  the 
recognition  of  the  genus.  In  the  genus  Productus  these  markings  are  al- 
ways clear  cut  and  well  defined,  while  in  Productella  there  is  commonly 
an  indefiniteness  about  them  which  is  in  strong  contrast  to  the  condition 
in  Productus.  In  Productella  the  radiating  markings  are  commonly  more 
or  less  discontinuous,  often  elongate,  node-like  elevations  of  the  surface, 
rather  than  distinct,  continuous  costffi.  The  surface  spines  are  also  com- 
monly arranged  in  a  more  or  less  irregular  manner  in  Productella,  while 
in  Productus  each  species  exhibits  a  fairly  definite  arrangement  of  its 
surface  spines. 

Pkodijctella  concentrica  (Hall) 
Plate  XIX,  Figs.  22-34 

1857.  Productus  concentricus  Hall,  10th  Rep.  N.  Y.  State  Cab.  Nat.  Hist., 

1).  180. 

1858.  Productus  shumardianus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  499,  pi.  7, 

fig.  1  (not  pi.  3,  fig.  9). 
1858.    Productus  concentricus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  517,  pi.  7, 

fig.  3. 
1860.     Productus  Cooperensis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1, 

p.  640. 
1862.     Producta  concentrica  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  411. 
1865.     Producta  concentrica  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  114. 
1865.     Producta  Cooperensis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  115. 
1867.     Productella  shumardiana  Hall,  Pal.  N.  Y.,  vol.  4,  p.  157,  pi.  23, 

figs.  6-8. 

1869.  Producta  concentrica  Winchell,  Safford's  Geol.  Tenn.,  p.  443. 

1870.  Producta  concentrica  Winchell,  Proc.  Am.  Phil.  Soc,  vol.  11,  p.  249. 
1888.     Productus  concentricus  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol. 

3,  p.  33,  pi.  6,  fig.  16. 

1888.  Productus  {Productella)  shumardianus  Herrick,  Bull.  Sci.  Lab.  Den- 
ison Univ.,  vol.  3,  p.  32,  pi.  7,  fig.  18;  pi.  12,  figs.  6,  43. 

1892.  Productella  Shumardiana  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 
pi.  17,  fig.  7. 

1899.  Productella  cooperensis  Girty,  Mon.  U.  S.  Geol.  Survey  No.  32,  p. 
528,  pi.  68,  figs.  8a-c,  9a-b. 

1901.  Productella  concentrica  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
p.  184,  pi.  16,  figs.  12-14. 

Description.  —  Shell  below  medium  size,  length  and  width  sub-equal,  or 
a  little  longer  than  wide,  the  hinge-line  shorter  than  the  greatest  width, 
the  cardinal  extremities  angular.  The  dimensions  of  a  nearly  complete 
specimen  are :  length  from  hinge-line  to  front  margin  13  mm.,  length  from 
umbonal  region  of  pedicle  valve  to  front  margin  15  mm.,  greatest  width 
15  mm.,  length  of  hinge-line  11  mm.,  convexity  of  pedicle  valve  10.2  mm. 


I'Koni'CTELLA 


99 


Pedicle  valve  gibbous,  arched  from  the  umbonal  region  to  the  anterior 
margin  with  the  posterior  curvature  somewhat  more  convex  than  the 
anterior,  the  umbonal  region  prominent  and  strongly  protuberant  beyond 
the  binge-line,  the  surface  curving  abruptly  to  the  cardinal  margin  and 
less  abruptly  to  the  lateral  and  anterior  margins,  rather  abruptly  deflected 
towards  the  cardinal  extremities  to  form  small,  compressed  auriculations ; 
mesial  sinus  obsolete;  the  beak  strongly  incurved. 

Brachial  valve  moderately  concave  in  its  visceral  portion,  with  the 
cardinal  extremities  somewhat  deflected,  anteriorly  and  laterally  the 
valve  is  abruptly  curved,  or  subgeniculate  in  passing  from  the  visceral 
region  to  the  produced  portion  of  the  valve,  so  that  the  entire  valve  be- 
comes very  deeply  concave  at  maturity. 

Surface  of  both  valves  usually  marked  by  strong,  concentric,  wrinkle- 
like folds  in  the  visceral  region,  which  become  inconspicuous  or  obsolete 
upon  tbe  produced  portion  of  the  shell;  surface  of  the  pedicle  valve  more 
or  less  distinctly  marked  by  elongate  nodes,  especially  upon  the  produced 
portion  of  the  shell,  which  are  frequently  more  or  less  connected  longi- 
tudinally to  form  rather  broad,  rounded,  depressed,  longitudinal  cost* 
which  are  irregular  in  their  development,  and  not  infrequently  nearly 
obsolete;  the  brachial  valve  marked  by  shallow,  more  or  less  elongate  de- 
pressions which  are  at  times  connected  to  form  somewhat  discontinuous, 
longitudinal  furrows,  these  markings  being  more  conspicuous  upon  the 
produced  portion  of  the  valve  but  being  likewise  present  upon  the  visceral 
surface;  they  are  more  constant  than  the  corresponding  costre  of  the 
pedical  valve ;  entire  surface  of  both  valves  marked  by  fine,  concentric 
lines  of  growth. 

Remarks.  —  This  species  was  originally  described  from  an  external  im- 
pression of  a  brachial  valve  from  the  upper  yellow  Kinderhook  sandstone 
at  Burlington,  Iowa.  Productella  sh  umardiana  was  described  from  two  speci- 
mens, a  pedicle  valve  from  the  same  horizon  and  locality  from  which  the 
type  of  P.  concentrica  was  obtained,  and  a  brachial  valve  from  the  Lou- 
isiana limestone  of  Clarksville,  Missouri ;  the  first  of  these  specimens  is 
undoubtedly  a  member  of  the  same  species  as  the  type  of  P.  concentrica, 
while  the  second  specimen  is  an  example  of  P.  pyxidata.  Productus 
coopcrcnsis  was  described  from'  the  Chouteau  limestone  of  central  Missouri, 
where  it  is  a  common  species;  many  examples  of  both  the  brachial  and 
pedicle  valves  have  been  examined  and  they  exhibit  no  characters  by 
means  of  which  they  can  be  separated  from  P.  concentrica.  All  three  of 
these  forms,  except  one  of  the  type  specimens  of  P.  shumardiana  must 
be  considered  as  synonyms,  and  for  tbis  form  the  namt  P.  concentrica 
holds  priority.  It  has  sometimes  been  suggested  that  the  species  should 
be  made  to  include  also  /'.  pyxidata,  but  that  species  is  clearly  distinct, 
P.   concentrica  being  characterized  by   its  narrower   form  and  its  much 


100  MISSISSIPPIAN    BRACHIOPODA 

more  strongly  convex  pedicle  valve,  with  much  smaller  cardinal  aurieula- 
i ions,  the  surface  markings  of  the  two  shells  are  also  distinctly  different. 
The  species  agrees  more  closely  with  the  middle  Devonian  /'.  spinulicosta, 
and  ii  has  sometimes  been  suggested  that  these  two  forms  are  identical, 
both  having  the  same  general  form,  size,  and  surface  markings.  H  is  pos- 
sible thai  this  interpretation  should  be  held,  bul  for  the  present  these 
Mississippian  shells  will  he  considered  as  distincl  from  the  middle  Devon- 
ian form,  although  an  entirely  satisfactory  method  of  distinguishing  them 

cannot    he   pointed   out. 

The  species  exhibits  considerable  variation  in  size  and  in  the  strength 
of  the  development  of  the  surface  markings.  It  sometimes  attains  a 
length  and  width  of  "JO  mm.  or  more.  The  variation  in  the  surface  mark- 
ings is  more  conspicuous  in  Hie  longitudinal  features,  although  the  con- 
centric folds  of  the  visceral  portion  of  the  pedicle  valve  are  sometimes 
almost  obsolete;  the  surface  features  of  the  brachial  valve '  are  usually 
more  constant  than  those  of  the  pedicle  valve. 

Horizon,  — Kinderhook. 

Phodictella  pyxidata  Hall 
Plate  XIX,  Figs.  1-21 

1858.     Productus  pyxidatus  Hall.  Geol.  Iowa.  vol.  1,  pt.  2,  p. '498,  pi.  3, 

tigs.  8a-e. 
1858.     Produclus  sli  intiardiamts  Hall,  Geol.  Iowa.  vol.  1.  pt.  2,  p.  499,  pi.  3, 

fig.  9  (not  pi.  7,  tig.  1). 
1883.     Productclla  pyxidata  Hall,  Hep.  N.  Y.  State  Geol.  for  1882,  pi.  (17) 

48,  fig.  34. 
1892.     Productclla  pyxidata  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  1, 

pi.  21,  figs.  20,  23. 
1892.     Productclla  pyxidata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi. 

17,  fig.  34.  pi.  17A,  fig.  14. 
1894.     Productetta  pyxidata   Keves,  Mo.    Geol.    Surv.,  vol.    5,    p.  52,  pi. 

38,  figs.  4a-d. 
1908.     Productclla  pyxidata  Rowley.  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  77,  pi.  17,  figs.  5,  30-36. 

Description. — Shell  usually  below  medium  size,  and  wider  than  long,  sub- 
semielliptical  in  outline,  the  hinge-line  a  little  shorter  than  the  greatest 
width,  the  cardinal  extremities  rounded.  The  dimensions  of  a  nearly 
complete  specimen  of  average  size  are :  length  from  hinge-line  to  front 
margin  14.4  mm.,  length  from  umbonal  region  of  pedicle  valve  to  front 
margin  16.4  mm.,  greatest  width  19.1  mm.,  length  of  hinge-line  ±17  mm., 
convexity  of  pedicle  valve  17  mm.,  depth  of  visceral  cavity  4.6  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbonal  region  projecting  somewhat  beyond  the  hinge-line, 
the  surface  curving  abruptly  from  the  umbonal  region  to  the  cardinal 
margin,  curving  less  abruptly  to  the  lateral  margins  and  more  gently  to 


PKODUCTELLA  101 

the  anterior  margin,  strongly  and  rather  abruptly  compressed  towards  the 
cardinal   extremities;  mesial  sinus  obsolete;   beak  small   and   incurved. 

Brachial  valve  rather  deeply  concave,  with  the  surface  somewhat  de- 
flected towards  the  cardinal  extremities,  the  concavity  rather  narrow 
at  the  beak  and  broadening  rapidly  anteriorly.  Internally  the  cardinal 
process  is  rather  small,  bifid,  with  each  division  longitudinally  excavated 
upon  its  posterior  and  outer  surfaces;  from  the  base  of  the  cardinal  pro- 
cess a  pair  of  ill-defined,  low,  broadly  diverging  ridges  extend  for  one- 
third  or  more  the  distance  to  the  postero-lateral  margins,  their  posterior 
slopes  being  more  abrupt  and  constituting  the  rudimentary  dental 
sockets ;  a  broad,  low  ridge  extends  anteriorly  along  the  median  line  of  the 
valve  from  the  junction  of  the  two  diverging  ridges,  which  is  soon  ab- 
ruptly constricted  to  a  narrow  and  low  median  septum  reaching  to  or 
beyond  the  middle  of  the  valve ;  the  brachial  impressions  of  moderate 
strength,  usually  reaching  a  little  more  than  two-thirds  the  distance  from 
their  bases  to  the  lateral  and  anterior  margins;  the  inner  surface  covered 
throughout,  except  upon  the  brachial  impressions,  the  median  septum  and 
the  region  adjacent  to  the  base  of  the  cardinal  process,  by  closely  crowded 
papillae  or  tubercles,  arranged  more  or  less  definitely  in  radiating  series. 

Surface  of  both  valves  marked  by  more  or  less  crowded,  concentric 
lines  of  growth.  Spine  bases  exceedingly  variable  in  their  development; 
on  the  pedicle  valve  they  are  sometimes  nearly  absent  except  a  few  near 
the  caixlinal  margin,  and  again  they  are  more  or  less  crowded  and  usually 
arranged  in  radiating  series  over  the  entire  surface,  sometimes  they  are 
strong  and  elongate  and  the  radiate  arrangement  is  so  well  defined 
that  the  surface  of  the  valve  appears  almost  to  be  marked  by  radiating 
costaB;  upon  the  brachial  valve  the  spine  bases  are  never  so  conspicuous. 

Remarks. — This  is  a  highly  characteristic  species  from  the  Louisiana 
limestone,  and  while  it  is  exceedingly  variable  in  some  of  its  features, 
especially  its  sux*faee  markings,  it  is  so  different  from  other  species  of  our 
faunas  that  there  can  be  no  difficulty  in  recognizing  it. 

Horizon. — Louisiana  limestone. 

Productella  nummularis  (Winchell) 
Plate  XIX,  Figs.  39-41 

1863.     Strophalosia  f  nummularis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil., 

p.  4. 
1900.     Productella  nummularis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  71,  pi.  1,  figs.  9-10. 

Description  —  Shell  of  medium  size,  subcircular  in  outline,  a  little  wider 
than  long,  the  hinge-line  about  two-thirds  the  width  of  the  shell,  the 
cardinal  extremities  obtusely  subangular  or  a  little  rounded.  The  dimen- 
sions of  an  imperfect  pedicle  valve  are:   length  27  mm.,  width  ±24  mm., 


102  SIISSISSIPPIAN    BBACH10PODA 

convexity  7  nun.  The  dimensions  of  a  brachial  valve  arc;  length  21  mm., 
width  25  mm.,  length  of  binge-line  16  nun. 

Pedicle  valve  depressed  convex,  with  the  greatest  convexity  near  or 
posterior  to  the  middle,  the  surface  curving  with  a  gently  convex  curva- 
ture to  the  lateral  and  anterior  margins  and  somewhat  compressed  to- 
wards the  cardinal  extremities,  the  curvature  from  the  umbonal  region 
to  the  cardinal  margin  OD  each  side  of  the  beak  rather  abrupt,  the  um- 
bonal  region  only  very  slightly  produced  posteriorly  beyond  the  hinge- 
line;  mesial  sinus  obsolete;  beak  small  and  incurved. 

Brachial  valve  nearly  flat,  with  a  shallow,  narrow  concavity  at  the 
beak  whose  lateral  margins  diverge  rapidly  anteriorly  and  become  less 
well  defined;  mesial  fold  obsolete.  Internally  the  cardinal  process  is 
small  and  bifid,  Lying  in  the  plane  of  the  valve  and  projecting  beyond 
the  hinge-line  into  the  umbonal  cavity  of  the  opposite  valve;  a  low 
median  ridge  extends  from  the  base  of  the  cardinal  process  nearly  to  the 
middle  of  the  valve. 

The  surface  of  the  pedicle  valve  is  covered  by  innumerable,  fine  and 
delicate  spines  which  attain  a  length  of  5  mm.  or  more;  the  brachial  valve 
is  marked  throughout  by  small  crowded  pits  which  may  represent  the 
position  of  similar  fine  spines,  although  the  spines  themselves  have  not 
been  observed;  both  valves  marked  by  conspicuous  and  nearly  regular, 
concentric  lines  of  growth. 

Remarks.— In  the  condition  of  preservation  in  which  this  species  occurs, 
in  a  fine,  yellow  sandstone  of  the  Kinderhook,  the  fine  surface  spines  are 
rarely  discernable,  but  the  surface  of  the  pedicle  valve  possesses  a  finely 
granular  texture  which  is  more  or  less  conspicuous;  the  most  conspicuous 
surface  markings  are  the  very  regular  concentric  lines  of  growth.  The 
species  is  characterized  by  its  subcircular  outline,  being  truncated  on  the 
posterior  side  by  the  hinge-line;  by  the  depressed-convex  pedicle  valve 
and  the  nearly  flat  brachial  valve.  The  species  resembles  P.  pyxidata 
but  it  attains  a  larger  size,  with  relatively  shorter  hinge-line  and  with- 
very  different  surface  markings ;  the  brachial  valve  is  also  much  flatter. 

Horizon.— Chonopectus  sandstone  of  the  Kinderhook. 

Productella  subl^vis  n.  sp. 
Plate  LXXXIII,  Figs.  18-20 

Description. — Shell  large,  depressed  concavo-convex,  wider  than  long, 
the  hinge-line  a  little  shorter  than  the  greatest  width  of  the  shell,  lateral 
and  anterior  margins  describing  a  regular,  subelliptical  curve,  one  side 
of  the  ellipse,  that  on  the  posterior  side  of  the  shell,  being  incom- 
plete. The  dimensions  of  the  best  preserved  brachial  valve  observed, 
a  small  individual,  are :  length  25  mm.,  width  33  mm.,  convexity  8  mm., 


PRODUCTUS  103 

length  of  hinge-line  26  mm.  The  dimensions  of  a  larger  brachial  valve, 
more  nearly  the  usual  size  of  the  species,  are:  length  31  mm.,  width  42 
mm.,  concavity  8.5  mm.,  length  of  hinge-line  31.5  mm. 

The  pedicle  valve  is  regularly  convex  except  postero-laterally,  where 
the  surface  towards  the  cardinal  extremities  is  somewhat  depressed,  so 
that  the  curve  of  the  surface  from  the  highest  point  of  the  shell  to  the 
cardinal  angles  is  at  first  gently  convex  and  then  concave.  The  surface 
of  the  valve,  is  marked  by  obscure,  depressed,  elongate  nodes  indicating 
the  position  of  spine  bases,  these  nodes  are  more  numerous  towards  the 
front  of  the  shell,  the  posterior  portion  being  almost  entirely  free  from 
them  in  the  best  specimens  observed. 

The  concavity  of  the  brachial  valve  follows  rather  closely  the  curve  of 
the  pedicle  valve  so  that  the  visceral  cavity  is  very  shallow,  the  surface  of 
this  valve  seems  to  be  more  completely  covered  with  the  obscure,  elongate 
spine  bases  than  the  pedicle  valve,  and  it  is  also  marked  by  faint  concen- 
tric lines,  especially  towards  the  cardinal  line. 

Remarks. — This  species  is  one  of  the  more  common  forms  in  the  yellow 
sandstone  at  Kinderhook,  Illinois,  but  most  of  the  specimens  observed 
have  been  somewhat  weathered,  so  that  but  little  more  than  the  general 
form  and  proportions  can  be  recognized.  Those  specimens  that  do  pre- 
serve the  surface  characters,  however,  show  that  the  shell  was  exception- 
ally smooth  for  members  of  this  genus,  the  node-like  spine  bases  being 
rather  obscure  in  all  cases.  The  species  is  larger  than  any  of  the  hereto- 
fore recognized  Kinderhook  species,  and  is  equalled  in  size  by  but  few 
Devonian  forms.  It  resembles  P.  onusta  Hall  from  the  Chemung  beds  of 
New  York,  but  is  less  convex,  with  a  proportionally  shorter  hinge-line,  it 
also  attains  a  larger  size  than  that  species,  judging  from  the  illustrations 
published  by  Hall.1 

Horizon. — Kinderhook. 

Genus  PRODUCTUS  Sowerby 

Description. — Shells  varying  in  size  from  small  to  very  large,  deeply 
concavo-convex  in  form,  usually  produced  anteriorly,  the  hinge-line 
straight  and  usually  equaling  the  greatest  width  of  the  shell,  commonly 
auriculate  at  the  cardinal  extremities.  Pedicle  valve  without  cardinal 
area  or  hinge-teeth,  the  two  valves  held  together  at  the  cardinal  margin 
by  the  strongly  incurved  beak  of  the  pedicle  valve.  Brachial  valve  more 
or  less  concave,  or  nearly  flat  in  the  visceral  region,  becoming  more 
strongly  curved  towards  the  anterior  and  lateral  margins ;  cardinal  area, 
dental  sockets  and  socket  plates  absent  or  very  rudimenfary,  the  cardinal 
process  large  and  strong,  extending  far  beyond  the    hinge-line    into  the 

lPal.  N.  Y,  vol.  4,  pi.  26,  figs.  29-42   (1867). 


KM  \i  ississi  I'IMA  x    BRACHIOPODA 

umbonal  cavity  of  the  opposite  valve.  Surface  of  both  valves  marked  by 
distinct,  subequal,  regular  or  flexuose,  and  usually  continuous  radiating 
costse,  and  l>\  concentric  undulations  or  wrinkles  which  are  commonly 
restricted  to  the  posterior  portion  of  the  valves  or  to  the  region  towards 

the  cardinal  extremities.  More  or  less  elongate,  hollow  spines  are  pres- 
enl  in  various  situations  upon  the  shell  surface,  usually  most  conspicu- 
ously developed  in  the  region  of  the  cardinal  extremities. 

Remarks.  The  genus  Productus  includes  one  of  the  largest  groups 
of  species  of  any  genus  of  J\l  ississippian  brachiopods,  and,  as  heretofore 
commonly  interpreted,  has  been  made  to  include  several  more  or  less 
widely  diverse  types  of  shells.  One  of  these  subordinate  groups  of 
species,  thai  typified  by  /'.  biseriatus  and  P.  punctatus,  has  been  separ- 
ated from  Productus  in  the  present  reporl  as  a  distinct  genus  under  the 
name  Echinoconchus.  Still  another  subordinate  group,  of  which  P.  cora 
is  a  typical  representative,  might  also,  perhaps,  be  made  to  constitute  a 
distinct  genus,  although  thai  has  not  been  done  here.  Recently  one  of 
our  species,   /'.   elegans,  has   been    made  the   type    of    still     another  genus, 

Diaphragmus,  by  Girty. 

Productus  burungtonensis   Hall 
Plate  IX,  Figs.  1-10 

L858.     Productus   flemingi  var.  burlingtonensis  Hall,   Geol.  Iowa,  vol.  1, 

pt.  2,  p.  598,  pi.  12,  figs.  3a-g. 
1883.     Product  us  Flemingi  var.  Burlingtonensis  Hall,  Rep.  N.  Y.   State 

Geol.  for  1882,  pi.  (18)  49,  figs.  6-8. 
1892.     Productus   Flemingi   var.   Bitrlingtonensis   Hall   and     Clarke,    Pal. 

N.  Y.,  vol.  8,  pt.  1,  pi.  18,  figs.  6-8. 
1894.     Productus  burlingtonensis  Keyes,  Mo.  Geol  Surv.,  vol.  5,  p.  41. 

Description. — Shell  of  medium  size  or  somewhat  larger,  broader  than 
long,  the  hinge-line  equaling  or  greater  than  the  greatest  width  of  the 
body  of  the  shell,  the  lateral  margins  sinuate  in  front  of  the  cardinal  ex- 
tremities, convexly  rounding  anteriorly  into  the  anterior  margin  which  is 
sinuate  in  its  central  portion.  The  dimensions  of  a  nearly  complete 
pedicle  valve  are :  length  from  the  hinge-line  to  the  anterior  margin  24 
mm.,  length  from  the  umbonal  region  to  the  anterior  margin  33  mm., 
length  of  hinge-line  41.5  mm.,  width  of  body  of  shell  at  its  mid-length  36 
mm.,  convexity  of  pedicle  valve  25  mm. 

Pedicle  valve  strongly  ventricose,  the  umbonal  region  protruding  con- 
spicuously posteriorly  beyond  the  hinge-line,  the  beak  strongly  incurved 
so  that  it  lies  nearly  opposite  the  center  of  the  valve,  the  surface  curving 
abruptly  to  the  cardinal  and  lateral  margins  and  a  little  more  gently  to 
the  anterior  margin,  auriculate  at  the  cardinal  extremities,  the  auricula- 
tions  of  moderate  size  and  rather  abruptly  differentiated  from  the  body  of 
the  valve,   their  surface   convex   antero-posteriorly   with   the   curvature 


PRODUCTUS  105 

more  abrupl  to  the  cardinal  margin;  mesial  sinus  originating  in  the  urn- 
bona]  region,  of  only  moderate  depth  and  width,  rounded  in  the  bottom 
and  ill  defined  laterally.  Surface  of  the  valve  marked  by  rounded, 
radiating  costs  which  increase  by  bifurcation  and  intercalation  poster- 
iorly, Inil  anterior  to  the  middle  they  usually  continue  without  further 
division  to  near  the  trout  margin,  where  they  tend  to  become  obsolete,  the 
distance  between  the  costa>  varies  from. 5  to  1.5  mm.  in  the  anterior  portion 
of  the  valve,  about  1  mm.  being  the  usual  distance  from  center  to  center, 
posteriorly  they  are  more  closely  crowded ;  on  the  posterior  slope  of  the 
valve  the  radiating  costse  are  crossed  by  distinct,  rather  regular,  wrinkle- 
like concentric  markings,  giving  to  that  portion  of  the  valve  a  distinctly 
semireticulate  ornamentation ;  spine  bases  are  either  nearly  obsolete  upon 
1  he  surface  of  the  valve  or  they  are  scattered  irregularly  upon  the  anterior 
and  lateral  slopes,  one  or  more  sometimes  being  present  upon  the  auricu- 
lar extensions  of  the  valve;  in  front  of  the  spine  bases,  when  present, 
two  or  more  of  the  surface  costse  are  sometimes  united  to  form  a  broader 
costa  which  continues  to  the  anterior  margin.  Internal  characters  of  the 
pedicle  valve  not  observed. 

Brachial  valve  gently  concave  in  its  posterior  portion,  flattened  towards 
the  cardinal  extremities  opposite  the  auriculations  of  the  other  valve, 
anteriorly  and  antero-laterally  the  valve  is  more  abruptly  curved  and  is 
produced  nearly  in  contact  with  the  anterior  and  antero-lateral  portions 
of  the  opposite  valve ;  anteriorly  the  mesial  portion  of  the  valve  is  elevated 
in  a  low,  rounded,  mesial  fold  to  correspond  with  the  sinus  of  the  oppo- 
site valve.  Surface  of  the  valve  marked  by  radiating  costaa  which  are 
less  distinctly  developed  than  those  of  the  opposite  valve,  and  in  the 
posterior  portion  by  concentric,  wrinkle-like  markings  which  are  also 
less  distinct  than  those  of  the  pedicle  valve ;  no  spine  bases  have  been 
observed  upon  this  valve,  although  they  may  be  present  in  some  cases. 
Internally  the  cardinal  process  is  large  and  strong,  its  entire  length 
being  produced  posteriorly  beyond  the  hinge-line  into  the  protuberant 
umbonal  portion  of  the  opposite  valve ;  it  is  bifid  at  its  extremity  and  is 
flanked  at  its  base  by  a  thickened  ridge  on  either  side  which  extends 
laterally  nearly  parallel  with  and  close  to  the  cardinal  margin,  distally 
these  lateral  ridges  become  broader  and  less  differentiated  from  the 
general  surface  of  the  valve,  but  the  thickening  extends  to  the  cardinal 
extremities ;  anteriorly  from  the  cardinal  process  a  low,  thin  median  sep- 
tum reaches  to  near  the  middle  of  the  valve ;  on  either  side  of  the  median 
line  where  the  valve  begins  to  approach  more  nearly  to  the  curvature 
of  the  opposite  valve,  the  inner  surface  is  covered  with  fine,  crowded, 
spinule-like  papilla?  which  are  inclined  anteriorly. 

Remarks. — This  species  is  characterized  by  the  strongly  convex  pedicle 
valve,  the  deep  visceral  cavity  between  the  two  valves,  the  usually  small 


L06  UISSISSII'I'IAN     BKACIIIOPODA 

auricular  extensions  of  the  pedicle  valve,  and  die  presence  of  a  mesial 
sinus.  Th  auricular  extensions  of  the  shell  are  usually  more  or  less 
imperfectly  preserved  and  oftentimes  appear  to  be  essentially  wanting, 
and  in  such  examples  the  hinge-line  is  apparently  shorter  than  the  great- 
est width  as  stilted  by  Hall  iii  the  original  definition  of  the  species, 
but  in  all  specimens  examined  in  which  the  auricular  extensions  are 
completely  preserved,  the  hinge-line  is  longer  than  the  width  of  the  shell 
anteriorly.  The  species  most  closely  resembles  /'.  iiiflatus,  but  in  that 
species  the  auricular  extensions  are  somewhat  more  conspicuous,  the 
mesial  sinus  is  usually  narrower  and  deeper,  and  the  semireticulate 
markings  of  the  posterior  portion  of  the  pedicle  valve  are  much  less 
conspicuous. 

Horizon. — Burlington  limestone. 

Productus  feknglenensis  Weller 
Plate  IX,  Figs.  11-17 

1909.     Productus  fernglenensis  Weller,  Bull.    Geol.    Soc.    Am.,    vol.    20, 
p.  299,  pi.  12,  figs.  14-17. 

Description. — Shell  of  medium  size  or  a  little  larger,  wider  than  long 
in  most  specimens,  but  sometimes  becoming  longer  than  wide  in  old 
examples,  hinge-line  a  little  shorter  than  the  greatest  width,  the  anterior 
margin  regularly  rounded  or  sometimes  a  little  sinuate  in  the  middle. 
The  dimensions  of  an  incomplete  specimen  are:  length  from  hinge-line 
to  front  margin  21.3  mm.,  length  from  umbonal  region  to  front  margin 
27  mm.,  length  of  hinge-line  27.5  mm.,  greatest  width  33.5  mm.,  convexity 
of  pedicle  valve  23  mm.  The  largest  specimen  observed  has  a  length  of 
39  mm.  from  the  umbonal  region  to  the  front  margin,  with  a  width  of 
35  mm. 

Pedicle  valve  gibbous,  the  umbonal  region  broadly  pointed  towards 
the  beak  and  strongly  protuberant  beyond  the  hinge-line,  the  mesial 
portion  of  the  valve  broadly  flattened  from  the  umbonal  region  to  the 
front,  the  surface  very  gently  convex,  nearly  straight  or  slightly  con- 
cave transversely,  rounding  more  abruptly  into  the  lateral  slopes  which 
drop  nearly  vertically  to  the  lateral  margins,  the  auriculations  small 
but  rather  well  defined  from  the  lateral  slopes ;  mesial  sinus  wanting 
or  only  slightly  depressed,  and  ill  defined  laterally;  the  beak  strongly 
incurved.  Surface  covered  by  rounded,  radiating  costas,  usually  1  mm. 
or  less  in  width,  which  increase  by  bifurcation  upon  the  posterior  slope, 
on  the  anterior  slope  they  either  continue  without  division  or  sometimes 
break  up  into  two  or  more  in  front  of  the  spine  bases  and  continue  to  the 
front  with  a  fasciculate  arrangement,  often  becoming  coalescent  near 
the  margin ;  upon  the  posterior  slope  the  radiating  costae  are  crossed  by 
rather  conspicuous,   concentric,   wrinkle-like   markings   which   are   com-' 


PRODUCTUS  107 

inonly  stronger  towards  the  cardinal  margins,  giving  to  this  portion  of 
the  valve  a  decidedly  semireticulate  appearance ;  the  entire  surface, 
when  well  preserved,  marked  by  fine  concentric  lines  of  growth.  Spine 
bases  usually  inconspicuous,  sometimes  apparently  absent,  when  present 
they  are  rather  coarse  and  occur  almost  entirely  upon  the  anterior  and 
lateral  slopes  of  the  valve  with  occasionally  one  or  more  upon  each 
auriculation. 

Brachial  valve  flattened  in  the  visceral  portion  with  the  auricular 
portions  only  slightly  differentiated,  becoming  more  concave  antez'iorly 
and  laterally  and  with  the  marginal  produced  region  curving  rather 
abruptly  to  conform  with  the  anterior  and  lateral  portions  of  the  oppo- 
site valve ;  mesial  fold,  when  present,  originating  posterior  to  the  middle 
of  the  valve,  it  is  low,  broad  and  illdefined  laterally,  not  infrequently 
absent.  Surface  marked  by  radiating  cost«  similar  to  those  of  the  oppo- 
site valve,  and  in  the  visceral  portion  by  well  defined,  concentric,  wrinkle- 
like markings  which  make  it  distinctly  semireticulate.  Internally  the 
cardinal  process  is  rather  short,  subtriangular  in  form  with  a  median 
groove  which  does  not  divide  it  into  two  distinct  lobes;  it  projects  poster- 
iorly into  the  umbonal  cavity  of  the  opposite  valve ;  other  internal  char- 
acters not  well  preserved. 

Remarks. — This  species  resembles  P.  burlingtonensis  in  general  form 
and  size,  but  it  differs  from  that  species  in  the  lower  curvature  of  the 
pedicle  valve,  and  especially  in  the  absence  or  slight  development  of 
the  mesial  sinus  of  the  pedicle  valve.  The  fasciculate  arrangement  of 
the  plications  anterior  to  the  base  of  surface  spines  upon  the  anterior 
slope  is  also  a  character  which  differentiates  the  species  from  P. 
burlingtonensis,  although  it  is  a  character  which  is  not  uniformly  present. 
The  species  differs  from  P.  costatus  of  the  Pennsylvanian  faunas,  in  the 
smaller  auriculations  and  in  the  absence  of  the  row  of  spine  bases,  which 
in  that  species  marks  the  inner  margin  of  each  auriculation. 

Horizon.— Fern  Glen  formation  and  Pierson  limestone  of  the  Kinder- 
hook. 

Productus  arcuatus  Hall 

Plate  XIII,  Figs.  1-8 ;  ?9-12 

1858.     Productus  arcuatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  518,  pi.  7, 

figs.  4a-b. 
1870.     Producta  arcuata  Winchell.  Proc.  Am.  Phil.  Soc,  vol.  11,  p.  250. 
1883.     Productella  arcuata  Hall,  Rep.  N.  Y.  State  Geol.,  for  1882,  pi.  (17) 

48,  figs.  31,  32. 
1888.     Productus  arcuatus  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3,  p. 

31,  pi.  3,  fig.  18. 
1892.     Productella  arcuata  Hall  and  Clarke.  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  17. 

figs.  31,  32. 
1894.     Productus  arcuatus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  40. 


108  Mississippi. \x    BBACHIOPODA 

1901.     Productus   arcuatus   Weller,    Trans.    St.   Louis   Acad.    Sci,   vol   11, 
p.  160,  pi.  14,  fig.  23;  ]>.  185,  pi.  16,  fig.  15. 

Dcscri/ilion.  Shell  below  medium  size,  usually  longer  than  wide,  the 
greatesl  width  near  the  mid-length,  the  hin^c  line  shorter  than  the 
greatesl   width,  the  cardinal  extremities  angular  or  sometimes  a  little 

rounded.  The  dimensions  of  a  nearly  perl'eel  pedicle  valve  are:  length 
from  hinge  line  to  front  margin  15.5  nun.,  length  from  umbonal  region 
to  front  margin  20.3  mm.,  greatest  width  1!)  mm.,  length  of  hinge-line 
14  nun.,  convexity   12.5   nun. 

Pedicle  valve  gibbous,  arched  longitudinally  with  the  longer  curve  on 
the  anterior  side,  the  umbonal  region  rather  broad  and  strongly  pro- 
tuberant beyond  the  hinge-line,  the  mesial  portion  of  the  valve  rather 
broadly  flattened  or  very  gently  convex  transversely,  the  lateral  slopes 
curving  abruptly  to  the  lateral  and  cardinal  margins,  the  auricula- 
tions  at  the  cardinal  extremities  small,  flattened  vertically  in  mature 
shells  but  in  young  individuals  the  surface  of  the  ambulations  is  more 
nearly  horizontal;  mesial  sinus  obsolete;  beak  strongly  incurved.  Surface 
of  the  valve  covered  by  rounded,  radiating  costa',  usually  measuring  about 
1  mm.  from  center  to  center  upon  the  anterior  slope,  they  increase  usually 
by  bifurcation  upon  the  posterior  slope  of  the  valve  and  continue  across 
the  anterior  slope  either  without  division  or  rarely  dividing,  occasionally 
two  eostse  coalesce  towards  the  margin  of  the  valve;  on  the  posterior 
slope  concentric,  wrinkle-like  markings  are  present,  best  developed  to- 
wards the  cardinal  margin  and  becoming  fainter  across  the  median  por- 
tion of  the  valve;  the  entire  surface  covered  by  fine,  concentric  lines 
of  growth  when  the  shell  is  not  exfoliated.  Spine  bases  usually  not  con- 
spicuous, sparsely  scattered  over  the  entire  surface  but  becoming  more 
abundant  upon  the  outer  half  of  the  valve.    Internal  characters  not  seen. 

Brachial  valve  not  observed. 

Remarks.— This  species  is  characterized  by  its  small  size,  the  great  con- 
vexity of  the  pedicle  valve  with  the  nearly  vertical  lateral  slopes,  the 
absence  of  a  mesial  sinus,  the  short  hinge-line,  and  small  auriculations 
whose  surface  is  more  nearly  vertical  than  horizontal.  In  some  respects 
the  shell  resembles  a  small  example  of  P.  burlingtonensis  but  it  differs 
from  that  species  in  the  absence  of  a  median  sinus  and  in  the  vertical 
flattening  of  the  auriculations. 

Horizon. — Kinderhook. 

Peoductus  sedaliensis  n.  sp. 
Plate  XIV,  Figs.  1-7 

1891.  Productus  blairi  Miller,  Adv.  Sheets  17th  Rep.  Geol.  Surv    Ind 

p.  79,  pi.  13,  fig.  17  (not  fig.  16). 

1892.  Productus  blairi  Miller,  17th  Rep.  Geol.  Surv.  Ind.,  p.  689,  pi   13 

fig.  17   (not  fig.  16). 


PRODUCTUS  1  <  19 

Description. — Shell  of  medium  size  or  somewhat  larger,  broader  than 
long,  the  hinge-line  shorter  than  the  greatest  width.  The  dimensions  of 
a  nearly  complete  specimen  are :  length  from  hinge-line  to  front  margin 
28.5  mm.,  length  from  umbonal  region  to  front  margin  33  mm.,  length 
of  hinge-line  2!>  mm.,  greatest  width  36  mm.,  convexity  of  pedicle  valve 
22.5  mm. 

Pedicle  valve  gibbous,  arched  from  the  umbonal  region  to  the  front 
margin  with  the  curvature  shorter  and  a  little  more  abrupt  posteriorly, 
the  umbonal  region  rather  broadly  pointed  towards  the  beak  and  pro- 
duced prominently  beyond  the  hinge-line,  the  median  portion  of  the  valve 
broadly  flattened  from  the  umbonal  region  to  the  anterior  margin,  this 
surface  curving  abruptly  into  the  lateral  slopes,  distinctly  flaring  towards 
the  lateral  and  anterior  margins,  the  auriculations  of  moderate  size  and 
not  abruptly  differentiated  from  the  lateral  slopes ;  mesial  sinus  obsolete ; 
beak  strongly  incurved.  Surface  marked  by  strong,  rounded,  radiating 
costse  which  divide  frequently  upon  the  posterior  slope,  rarely  or  not  at  all 
upon  the  anterior  and  lateral  slopes,  until  approaching  the  flaring  margins, 
where  bifurcations  again  occur,  the  size  of  the  costas  upon  the  anterior 
slope  is  usually  about  1  mm.  or  somewhat  more  from  center  to  center  ; 
crossing  the  radiating  costoe  upon  the  posterior  slope  of  the  shell  are  more 
or  less  conspicuous,  concentric,  wrinkle-like  markings  which  give  to  that 
surface  a  distinctly  semireticulate  appearance;  the  entire  surface,  when 
well  preserved,  covered  by  faint,  concentric  lines  of  growth.  Spine  bases 
usually  inconspicuous,  when  best  preserved  they  are  scattered  somewhat 
sparsely  over  the  anterior  and  lateral  slopes,  with  sometimes,  and  perhaps 
always  if  well  preserved,  a  row  along  the  cardinal  margin. 

Brachial  valve  gently  concave  in  the  visceral  region  with  the  auricular 
portions  rather  broad  but  not  sharply  defined,  anteriorly  and  laterally 
the  curvature  becomes  greater  as  the  surface  passes  into  the  produced 
portion  lying  in  contact  with  the  opposite  valve ;  the  mesial  portion  of 
the  valve,  from  near  the  middle  of  the  visceral  region,  is  usually  slightly 
raised  above  the  surface  on  either  side  in  a  slight,  rather  broad,  ill- 
defined  mesial  fold.  Surface  marked  by  radiating  series  of  somewhat 
elongate  pits  near  the  beak,  which  are  interrupted  intercostal  furrows, 
but  the  markings  quickly  change  into  distinct  and  rather  strong  radiating 
costae  similar  to  those  of  the  opposite  valve,  which  increase  by  bifurcation 
and  intercalation ;  the  visceral  portion  of  the  valve  crossed  by  concentric 
wrinkle-like  markings,  and  the  entire  surface  crossed  by  fine,  concentric 
lines  of  growth  which  are  much  stronger  than  those  of  the  opposite  valve. 

Remarks.— Miller  interpreted  an  external  impression  of  a  brachial  valve 
of  this  species  as  a  pedicle  valve  of  his  species  P.  blairi,  and  illustrated 
it  as  one  of  the  types  of  that  species.  The  specimen  figured  by  Miller 
as  an  external   impression  of  the  brachial  valve  of  P.   blairi  is  properly 


110  MISSISSIITIAN    BRACHIOPODA 

i ti t i'i| nil t'd  and  may  consequently  be  assumed  as  the  type  of  that  species. 
The  specimen  incorrectly  interpreted  by  Miller  belongs  to  the  hitherto 
undefined  species  here  described.  This  species  resembles  both  P.  bur- 
lingtonensis  and  /'.  ft rnglcncnsis  in  some  respects,  but  is  clearly  distinct 
from  either.  It  can  at  once  be  distinguished  from  P.  femglentnsis  by  its 
somewhat  coarser  costal,  by  the  entire  absence  of  mesial  sinus,  by  the 
distinctly  flaring  lateral  and  anterior  margins,  and  by  the  more  or  less 
interrupted  intercostal  furrows  towards  the  beak  of  the  brachial  valve. 
Tu  the  Last  character  the  species  resembles  P.  blairi,  but  in  that  species 
the  interruption  of  the  intercostal  furrows  continues  throughout  the 
entire  valve,  they  being  essentially  absent  altogether  towards  the  beak. 
Horizon. — Chouteau  limestone. 

Productus  blairi  Miller 
Plate  XIV,  Pigs.  14-21 

1891.  Productus  blairi  Miller,  Adv.   Sheets  17th  Rep.  Geol.   Surv.  Ind., 

p.  79,  pi.  13,  fig.  16  (not  fig.  17). 

1892.  Productus  blairi  Miller,  17th  Rep.  Geol.  Surv.  Ind.,  p.  689,  pi.  13, 

fig.  16  (not  fig.  17). 

Description. — Shell  of  medium  size  or  smaller,  wider  than  long,  the 
hinge-line  shorter  than  the  greatest  width,  the  greatest  width  at  about  the 
mid-length.  The  dimensions  of  a  nearly  complete  specimen  are;  length 
from  hinge-line  to  anterior  margin  20  mm.,  length  from  umbonal  region 
to  anterior  margin  22.4  mm.,  greatest  width  25.2  mm.,  length  of  hinge-line 
21  mm.,  convexity  of  pedicle  valve  -4-12  mm.,  depth  of  visceral  cavity 
between  the  two  valves  10  mm. 

Pedicle  valve  strongly  convex  in  mature  specimens,  the  umbonal 
region  rather  broad  and  moderately  produced  beyond  the  hinge-line,  the 
surface  arched  from  the  umbonal  region  to  the  front,  the  median  portion 
of  the  valve  rather  broadly  flattened  with  the  lateral  slopes  curving  more 
abruptly  to  the  lateral  margins,  the  auriculations  of  moderate  size,  rather 
sharply  differentiated  and  distinctly  compressed  horizontally ;  mesial 
sinus  very  shallow,  rather  broad  and  ill-defined,  originating  in  the  um- 
bonal region ;  beak  small,  strongly  incurved.  Surface  marked  by  strong, 
radiating  costa?  which  are  interrupted  upon  the  posterior  slope  of  the 
valve  and  to  some  extent  anteriorly,  so  as  to  appear  as  series  of  elongate 
nodes ;  the  posterior  half  of  the  valve  is  crossed  by  strong,  concentric, 
wrinkle-like  markings  which  become  more  conspicuous  towards  the  car- 
dinal auriculations;  fine  concentric  lines  of  growth  also  cover  the  entire 
surface  of  the  valve  when  it  is  well  preserved.  Spine  bases  not  conspicu- 
ous unless  the  node-like  interrupted  portions  of  the  radiating  costse  each 
bore  a  spine,  as  is  perhaps  the  ease. 


PRODUCTUS  111 

Brachial  valve  gently  concave  throughout  the  visceral  portion  with 
the  auriculations  somewhat  deflected,  anteriorly  and  laterally  the  con- 
cavity becomes  greater  as  the  curvature  of  the  valve  comes  more  nearly 
in  conformity  with  the  margin  of  the  other  valve  in  its  produced  portion ; 
the  mesial  portion  of  the  valve  sometimes  slightly  elevated  in  its  anterior 
half,  in  a  low,  obscure,  mesial  fold.  Surface  nearly  free  from  radiating 
markings  towards  the  beak,  but  marked  beyond  this  clear  space  by  radiat- 
ing series  of  elongated  pits  which  are  essentially  discontinuous,  radiating, 
intercostal  furrows;  rather  strong,  concentric,  wrinkle-like  markings  cover 
the  visceral  portion  of  the  valve,  and  finer  concentric  lines  of  growth 
cover  the  entire  surface. 

Remarks.— In  the  original  definition  of  this  species  Miller  referred  to 
two  specimens  which  he  illustrated  as  the  types.  One  of  these  specimens, 
the  original  of  the  first  of  the  two  illustrations,  was  correctly  interpreted 
as  an  external  impression  of  the  brachial  valve,  and  this  one  is  here  se- 
lected as  the  type  of  the  species.  The  second  specimen  illustrated,  and 
interpreted  as  the  internal  cast  of  the  pedicle  valve,  is  really  an  external 
impression  of  the  brachial  valve  of  quite  a  different  species  which  is  here 
described  as  P.  sedaliensis.  Miller  evidently  did  not  have,  and  had  not 
seen  the  true  pedicle  valve  of  his  species.  P.  blairi  differs  markedly  from 
other  species  of  the  genus  in  our  Mississippian  faunas  in  the  marked  in- 
terruption of  the  radiating  costal  of  the  pedicle  valve,  giving  the  appear- 
ance of  series  of  elongate  nodes,  and  in  the  interruption  of  the  intercostal 
furrows  of  the  brachial  valve,  giving  the  appearance  of  series  of  elongated 
pits.  This  style  of  ornamentation  strongly  suggests  a  relationship  to  some 
of  the  Upper  Devonian  species  which  have  been  referred  to  the  genus 
Productella,  and  it  is  possible  that  the  species  should  be  referred  to  that 
genus,  but  since  the  presence  or  absence  of  hinge-teeth  cannot  be  deter- 
mined in  any  of  the  specimens  examined,  the  species  is  allowed  to  re- 
main in  the  genus  Productus. 

Horizon.  —  Chouteau  limestone. 

Productus  inflatus  McChesney 
Plate  X,  Figs.  1-6 

1860.  Productus  inflatus  McChesney,  Desc.  New  Foss.,  p.  40. 
1865.  Productus  inflatus  McChesney,  111.  New  Spec.  Foss.,  pi.  6,  figs.  la-c. 
1868.  Productus  inflatus  McChesney,  Trans.  Chicago  Acad.  Sci.,  vol.  1, 
p.  27,  pi.  6,  figs.  la-c. 
Description.  —  Shell  of  medium  size  or  larger,  usually  longer  than  wide, 
the  greatest  width  along  the  hinge-line,  the  lateral  margins  a  little  sinuate, 
in  front  of  the  cardinal  extremities,  rounding  anteriorly  into  the  anterior 
margin  which  is  a  little  sinuate  in  the  middle.  The  dimensions  of  a  rather 
large  pedicle  valve  which  is  broader  than  usual  are :  length  from  hinge- 
line  to  anterior  margin  20.9  mm.,  length  from  umbonal  region  to  anterior 


112  \i  [SSISSIPP]  \\    BRACHIOPODA 

margin  28  mm.,  length  of  binge-line  ■>'>  mm.,  width  of  body  of  shell  at  its 
mid-length  29.3  nun.,  convexity  of  pedicle  valve  17  nun. 

Pedicle  valve  gibbous,  the  umbonal  region  conspicuously  protuberanl 
beyond  the  binge-line,  the  beat  strongly  incurved,  the  surface  curving 
abruptly  to  the  cardinal  margin  and  a  little  more  gently  to  the  lateral 
and  anterior  margins,  auriculate  at  the  cardinal  extremities,  the  auricula- 
t  ions  imt  sharply  differentiated  from  the  lateral  slopes,  rather  high  and 
arched  antero-posteriorly  with  the  curvature  a  little  more  abrupt  to  the 
cardinal  margin;  mesial  sinus  originating  iii  the  unilional  region,  rather 
narrow  and  of  moderate  depth.  Surface  of  valve  marked  by  rounded, 
radiating  costse  which  increase  by  bifurcation  on  the  posterior  slope  of  the 
valve,  usually  continuing  across  the  anterior  slope  without,  division, 
tending  to  become  fainter  or  nearly  obsolete  towards  the  margin,  From 
.">  nun.  to  1  mm.  apart  in  front,  usually  a  little  less  than  1  mm.,  becoming 
smaller  and  more  crowded  posteriorly  and  laterally;  crossing  the  radiat- 
ing costse  upon  the  posterior  slope  of  the  valve  are  concentric,  wrinkle-like 
markings  which  give  to  that  surface  a  scmich'culate  ornamentation;  spine 
bases  apparently  absent  or  very  sparsely  and  irregularly  scattered  upon 
the  body  of  the  shell,  but  when  the  shell  is  well  preserved  a  row  of  three 
or  four  rather  strong  spine  bases  is  present  near  and  parallel  with  the  car- 
dinal margin  on  each  side  of  the  beak.  Internal  characters  of  the  valve 
not  observed. 

Brachial  valve  only  imperfectly  known,  it  is  moderately  concave  in 
its  posterior  portion,  leaving  a  rather  deep  visceral  cavity  between  the 
two  valves,  becoming  more  strongly  curved  anteriorly  and  laterally  and 
approaching  closely  the  opposite  valve.  The  surface  markings  are  similar 
to  those  of  the  opposite  valve. 

I,'(  marks. — In  its  general  size  and  form  this  species  approaches  some- 
what closely  to  P.  burlingtonensis.  It  may  be  easily  distinguished  from 
that  species  by  its  less  depressed  or  more  inflated  auriculations  of  the 
pedicle  valve,  with  the  row  of  spine  bases  along  the  cardinal  margin,  by 
the  narrower  and  somewhat  more  sharply  defined  mesial  sinus  and  by  the 
somewhat  finer  radiating  costae.  The  row  of  spine  bases  along  the  cardinal 
margin  is  commonly  difficult  to  recognize  because  of  the  condition  of 
preservation  of  the  shells,  but  the  inflated  auriculations  are  easily  dis- 
tinguished in  almost  every  example  observed. 

Horizon. — Chester  group,  Okaw  formation. 

Productus  mesialis  Hall 
Plate  X,  Figs.  7-13 ;  Plate  LXXXIII.  Figs.  14-17 

1858.     Productus  mesialis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  636,  pi.  19, 

figs.  2a-c. 
1883.     Productus  mesialis  Hall.  Rep.  N.  Y.  State  Geol.  for  1882,  pi.  (18) 

49,  figs.  9-10. 


PROOUCTUS  113 

1892.     Productus  mesialis  Ball  and  Clarke,  Pal.  X.  Y.,  vol.  8.  pt.  1,  pi.  18, 
figs,  it-10. 

Description.  Shell  of  medium  size  or  smaller,  wider  than  long,  the 
greatesl  width  along  the  hinge-line.  The  dimensions  of  a  pedicle  valve, 
one  of  Hie  co-types,  are:  length  from  hinge-line  to  front  margin  20.2  mm., 
length  from  nmlmnal  region  to  front  margin  23  mm.,  width  along  hinge- 
line  31   mm.,   convexity  18   mm. 

Pedicle  valve  gibbous,  more  abruptly  curved  or  subgeniculate  near  the 
middle,  the  Lateral  slopes  dropping  abruptly  to  the  margins,  the  umbonal 
region  rather  broadly  pointed  and  moderately  protuberant  beyond  the 
binge-line,  towards  the  cardinal  extremities  the  surface  is  compressed  and 
extended  into  auriculations  of  moderate  size  which  usually  extend  some- 
what beyond  the  greatest  width  of  the  valve  anteriorly  and  are  convex 
antero-posteriorly  ;  mesial  sinus  originating  in  the  umbonal  region,  of  mod- 
erate width,  somewhat  variable  in  depth,  rounded  in  the  bottom  ;  the  beak 
pointed  and  incurved.  Surface  marked  by  rounded  radiating  costa?  from 
.5  mm  to  1  mm.  in  width,  which  commonly  increase  by  bifurcation  upon 
the  posterior  slope  and  less  frequently  or  not  at  all  upon  the  anterior 
slope,  sometimes  becoming  obsolescent  towards  the  front  and  lateral  mar- 
gins; the  posterior  slope  marked  by  concentric,  wrinkle-like  markings 
of  only  moderate  strength  or  rather  faint.  Spine  bases  rather  sparsely 
scattered  over  the  anterior  and  lateral  slopes  with  a  row  of  about  four 
on  each  side  of  the  beak  along  the  cardinal  margin,  with  sometimes  a 
few  additional  ones  upon  the  cardinal  auriculations. 

Brachial  valve  with  a  slight  concavity  towards  the  beak,  beyond  which 
it  is  nearly  flat  throughout  the  visceral  region,  bending  rather  abruptly 
into  the  produced  anterior  and  lateral  margins,  the  cardinal  auricula- 
tions only  moderately  differentiated  from  the  general  surface ;  towards 
the  front  of  the  visceral  surface  the  median  portion  of  the  valve  is  slightly 
elevated  in  an  obscure  median  fold  which  becomes  much  stronger  upon 
the  anterior  produced  portion  of  the  valve.  Surface  marked  by  radiating 
costa*  similar  to  those  of  the  opposite  valve  and  by  concentric,  wrinkle- 
like markings  which  are  commonly  rather  faint. 

I>'(  marks.— This  species  is  especially  characterized  by  the  subgeniculate 
curvature  of  the  pedicle  valve,  the  well  defined  mesial  sinus  of  the  same 
valve,  and  by  the  flattened  visceral  portion  of  the  brachial  valve.  In 
some  respects  the  shell  resembles  P.  burlingtoncnsis,  but  it  is  smaller  and 
broader,  with  less  regular  curvature  of  the  pedicle  valve,  and  much  flatter 
visceral  portion  of  the  brachial  valve.  The  depth  of  the  mesial  sinus  of 
the  pedicle  valve  is  a  somewhat  variable  character,  in  some  individuals 
being  almost  obsolete. 

Horizon.— Keokuk  limestone. 


114  MISSISSII'I'IAN    BHACIIIOI'ODA 

I'linl'K'TI'S    MKSK'OSTALIS    II.    sp. 

Plato  XI,  Figs.  12-16 

Description.-  Shell  of  medium  size  or  smaller,  broader  than  long,  the 
binge-line  apparently  a  Little  shorter  than  the  greatest  width.  The  di- 
mensions of  a  somewhal  incomplete  pedicle  valve  are:  length  from  hinge- 
line  to  anterior  margin  L6.2  mm.,  length  from  umbonal  region  to  anterior 
margin  17..")  mm.,  Length  of  binge-line  approximately  18  mm.,  greatest 
width  of  shell  22  mm.,  convexity  of  pedicle  valve  approximately  13  mm. 

Pedicle  valve  strongly  convex,  the  umbonal  region  only  moderately 
produced  beyond  the  liinge-liue,  the  beak  incurved,  the  surface  curving 
more  abruptly  to  the  cardinal  margin,  the  curvature  to  the  lateral  and 
anterior  margins  about  equal,  the  cardinal  auriculations  small;  mesial 
sinus  originating  in  the  umbonal  region,  shallow,  rather  narrow,  and  ill- 
delined  laterally.  Surface  of  the  valve  marked  by  rounded,  radiating 
plications,  increasing  by  bifurcation,  and  somewhat  irregular  in  size; 
along  the  median  line  is  one  plication  which  is  notably  larger  than  any 
of  the  others  and  which  is  bordered  on  either  side  by  a  broader  and 
deeper  furrow ;  on  the  posterior  surface  of  the  valve  the  radiating  mark- 
ings are  crossed  by  concentric  plications  which  are  fainter  in  the  median 
portion,  becoming  wrinkle-like  towards  the  cardinal  auriculations;  spine 
bases  not  distinctly  shown. 

Brachial  valve  gently  concave  posteriorly,  becoming  more  abruptly 
curved  anteriorly  and  antero-laterally,  being  produced  nearly  in  contact 
with  the  anterior  and  antero-lateral  portions  of  the  opposite  valve ;  ante- 
riorly the  mesial  portion  of  the  valve  is  raised  in  a  low  mesial  fold  to  cor- 
respond with  the  sinus  of  the  opposite  valve.  Surface  of  the  valve  marked 
by  radiating  plications  similar  to  those  of  the  opposite  valve. 

Remarks. — All  examples  of  this  species  which  have  come  under  ob- 
servation are  more  or  less  incomplete,  so  that  many  details  of  the  shell  are 
not  yet  satisfactorily  determined,  but  the  species  is  especially  character- 
ized by  the  conspicuous  mesial  plication  in  the  shallow  sinus  of  the  ped- 
icle valve,  and  no  difficulty  has  been  found  in  the  identification  of  any 
specimen. 

Horizo >u— English  River  Grit-stone  of  the  Kinderhook. 

Productus  viminalis  White 
Plate  XI,  Figs.  6-11 

1858.     Productus  setigerusf  var.  keokuk  Hall,  Geol.  Iowa,  vol.  1,  pt.  2, 

p.  639,  pi.  19,  figs.  4b-c. 
1862.     Productus  viminalis  "White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9, 

p.  29. 
1883.     Productus  semireticulatus  Hall,  Rep.  N.  Y.  State  Geol.  for  1882, 

pi.  (18),  49,  fig.  12  (not  11  and  13). 


PR<  1DUCTUS  115 

1892.     Productus  semireticulatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 
pi.  18.  fig.  12  (not  11  and  13). 

Description.— Shell  large,  as  long  or  longer  than  wide,  the  greatest 
width  near  the  mid-length,  the  hinge-line  shorter  than  the  greatest  width. 
The  dimensions  of  a  nearly  complete  pedicle  valve  are :  length  from 
hinge-line  to  front  margin  38.5  mm.,  length  from  umbonal  region  to  front 
margin  48  mm.,  greatest  width  47  mm.,  length  of  hinge-line  35  mm.,  con- 
vexity 29.5  mm. 

Pedicle  valve  gibbons,  arched  from  the  umbonal  region  to  the  front 
margin  with  the  posterior  curvature  a  little  more  abrupt,  the  umbonal  re- 
gion rather  narrow,  conspicuously  protuberant  beyond  the  hinge-line,  the 
mesial  portion  of  the  valve  broadly  flattened  from  the  umbonal  region  to 
the  front  margin,  the  lateral  slopes  curving  abruptly  to  the  lateral  and 
cardinal  margins,  the  auriculations  at  the  cardinal  extremities  very  small, 
the  lateral  and  anterior  margins  slightly  flaring;  mesial  sinus  slight,  some- 
times essentially  wanting,  shallow,  and  ill-defined  laterally  when  present ; 
beak  pointed,  strongly  incurved.  Surface  marked  by  rounded,  radiating 
costae  about  1  mm.  or  1.5  mm.  apart  upon  the  anterior  slope,  usually  be- 
coming coarser  and  more  or  less  coalescent  towards  the  anterior  margin, 
upon  the  posterior  slope  the  costa?  increase  frequently  by  bifurcation,  the 
divisions  becoming  much  less  frequent  upon  the  anterior  slope ;  upon  the 
posterior  slope  concentric,  wrinkle-like  markings  cross  the  radiating 
costa1,  giving  to  the  valve  a  semireticulate  style  of  ornamentation,  these 
markings  are  strongest  towards  the  cardinal  margin,  usually  becoming 
rather  faint  across  the  median  portion  of  the  valve ;  fine  but  rather  strong 
concentric  lines  of  growth  cover  the  entire  surface  of  the  valve  when  it  is 
not  exfoliated.  Spine  bases  are  inconspicuous  and  only  sparsely  scat- 
tered over  the  anterior  slope  of  the  valve,  but  just  inside  the  small  auric- 
ulations upon  the  lateral  slopes  of  the  valve,  there  is  a  large  group  of 
fine,  closely  crowded  spines.  The  inner  surface  of  the  valve  towards  the 
anterior  and  lateral  margins,  is  thickly  covered  by  rather  coarse  papillae 
or  tubercles  which  appear  as  pits  upon  the  surface  of  internal  casts. 

Brachial  valve  flattened  in  the  visceral  region,  more  concave  anteriorly 
and  laterally  and  becoming  moderately  produced  with  the  outer  margin 
of  the  opposite  valve ;  a  broad,  low,  ill-defined  mesial  fold  commonly  orig- 
inates near  the  center  of  the  valve  and  continues  to  the  anterior  margin. 
Surface  marked  by  radiating  costa?  similar  to  those  of  the  opposite  valve, 
and  in  its  visceral  part  by  concentric,  wrinkle-like  markings,  the  concen- 
tric lines  of  growth  similar  to  those  of  the  opposite  valve.  Spine  bases 
apparently  absent  upon  the  specimens  observed.  Internally  the  cardinal 
process  is  rather  small  and  bifid,  projecting  posteriorly  into  the  umbonal 
cavity  of  the  opposite  valve,  anteriorly  from  its  base  a  median  ridge  or 


1  16  MISSISSIPPI/^    BRACHIOPOD.A 

septum  extends  some  distance,  its  entire  Length  not  shown  in  the  only 
specimen  observed. 

Remarks. — The  example  of  this  species  whose  dimensions  are  given 
above  is  an  undersized  specimen,  some  large  shells  having  an  extreme 
length  of  65  mm.  or  more.  The  type  specimen  of  the  species,  from  the 
Burlington  limestone,  is  here  illustrated  for  the  first  time,  but  the  species 
also  occurs,  perhaps  even  more  commonly,  in  the  Keokuk  limestone. 

The  species  is  characterized  by  its  large  size,  its  small  auricular  exten- 
sions, its  somewhat  flaring  anterior  and  lateral  margins,  and  especially  by 
the  Large  groups  of  tine,  closely  crowded  spines  which  occur  on  the  lateral 
slopes  adjacent  lo  the  cardinal  extremities. 

Horizon. —  Burlington  and  Keokuk  Limestones. 

Productus  crawfobdsvillensis  n.  sp. 

Plate  XII,  Figs.  4-7 

1892.     Productus  magnus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  S,  pt.  1,  pi. 
17 A,  fig.  15  (not  P.  magnus.  M.  &  W.) 

Description. — Shell  above  medium  size,  broader  than  long,  the  greatest 
width  along  the  hinge-line,  the  anterior  margin  slightly  sinuate,  the  vis- 
ceral cavity  between  the  two  valves  rather  shallow.  The  dimensions  of  a 
nearly  complete  pedicle  valve  are:  length  from  hinge-line  to  front  margin 
36.6  mm.,  length  from  umbonal  region  to  front  margin  41.8  mm.,  width  47 
mm.,  convexity  30  mm. 

Pedicle  valve  strongly  convex,  the  longitudinal  curvature  subgeniculate 
a  little  back  of  the  line  between  the  visceral  and  produced  portions  of  the 
valve,  the  posterior  slope  gently  convex  with  the  umbonal  region  only 
moderately  protuberant  beyond  the  hinge-line,  compressed  towards  the 
cardinal  extremities,  the  anterior  slope  gently  convex,  the  surface  drop- 
ping abruptly  to  the  lateral  margins,  the  auriculations  small  and  com- 
pressed vertically ;  mesial  sinus  originating  near  the  middle  of  the  pos- 
terior slope,  rather  narrow,  shallow  and  rounded  in  the  bottom,  lying  in 
the  middle  of  a  rather  broad  region  which  is  gently  convex  on  each  side 
of  the  sinus  and  drops  away  rather  abruptly  into  the  lateral  slopes ;  the 
beak  small,  incurved,  but  scarcely  reaching  beyond  the  hinge-line.  Sur- 
face marked  by  rounded,  radiating  costaj  which  increase  by  frequent 
bifurcations  and  intercalations  upon  the  posterior  slope,  dividing  less 
frequently  or  sometimes  anastomosing  upon  the  anterior  slope  and  be- 
coming more  or  less  obsolete  towards  the  front  of  mature  examples,  where 
best  developed  upon  the  anterior  slope  they  are  usually  about  1  mm. 
apart  from  center  to  center ;  the  posterior  slope  of  the  valve  is  well 
marked  by  concentric,  wrinkle-like  markings,  giving  it  a  distinctly  semi- 
reticulate  appearance,  these  markings  often  being  more  strongly  defined 
towards  the  cardinal  margin  ;  the  entire  surface  is  marked  by  fine  but  per- 


PRODUCTUS  117 

fectly  distinct  lines  of  growth.  The  spine  hases  occur  in  a  rather  broad 
band  across  the  entire  valve  between  the  cardinal  extremities,  just  in 
front  of  the  subgeniculate  curvature  of  the  valve,  throughout  this  band 
rather  strong  spines  occur  more  or  less  uniformly  at  distances  of  from  3 
to  5  mm.,  along  the  cardinal  margin  a  row  of  from  5  to  8  spine  bases 
occur  on  each  side  of  the  beak,  increasing  in  size  distally  and  diverging 
slightly  from  the  cardinal  margin,  upon  the  posterior  slope  a  few  spine 
bases  are  sometimes  sparingly  scattered  but  upon  the  anterior  slope  they 
are  commonly  absent  beyond  the  band  already  described. 

Brachial  valve  gently  concave  throughout  the  visceral  region  but  curv- 
ing abruptly  into  the  produced  portion  anteriorly  and  laterally,  the 
auriculations  scarcely  or  not  at  all  differentiated  from  the  general  sur- 
face ;  mesial  fold  low,  narrow  and  ill-defined,  confined  almost  entirely  to 
the  anterior  produced  portion  of  the  valve.  Surface  marked  by  fre- 
quently dividing,  radiating  costas  similar  to  those  of  the  opposite  valve, 
which  become  more  or  less  obsolescent  upon  the  anterior  produced  por- 
tion of  the  valve,  and  by  similar,  wrinkle-like,  concentric  markings  upon 
the  visceral  portion,  also  throughout  by  fine  concentric  lines  of  growth. 
Spine  bases  seem  to  be  lacking  upon  this  valve.  Internally  the  cardinal 
process  is  rather  small  and  is  apparently  trifid,  extending  posteriorly 
from  the  cardinal  margin  into  the  umbonal  cavity  of  the  opposite  valve, 
anteriorly  from  the  base  of  the  cardinal  process  the  median  ridge  extends 
nearly  to  the  anterior  side  of  the  visceral  portion  of  the  valve,  the  brachial 
impressions  are  rather  widely  separated  and  extend  anteriorly  nearly  to 
the  edge  of  the  visceral  portion  of  the  valve. 

Remarks.  —  This  species  has  been  variously  identified  in  the  past  but  it 
is  apparently  a  well  characterized,  undefined  species.  It  may  be  easily 
recognized  by  the  suligeniculate  curvature  of  the  pedicle  valve,  with  the 
conspicuous  band  of  strong  spines  stretching  entirely  around  the  valve 
between  the  cardinal  extremities  and  just  in  front  of  the  geniculate  bend- 
ing of  the  valve,  and  by  the  row  of  spines  along  the  cardinal  margin. 
The  anterior  produced  portion  of  the  valve  is  proportionally  elongate,  and 
the  visceral  cavity  between  the  two  valves  consequently  rather  shallow, 
in  one  specimen  having  a  width  of  38  mm.,  the  depth  of  the  visceral  cavity 
being  only  10  mm. 

Horizon.— Keokuk  (Crawfordsville  beds,  Indiana). 

Productus  magnus  Meek  and  Worthen 
Plate  XV,  Figs.  1-8 

1861.     Productus  magnus  Meek  and  Worthen,  Proc.  Acad.  Nat.  Sci.  Phil., 

p.  142. 
1863.     Productus  Fcntonensis  Swallow,  Trans.  St.  Louis  Acad.  Nat.  Sci., 

vol.  2,  p.  93. 


lis  Mississii'i'i.w    BRACHIOPODA 

1868.     Prodi/el  us  magnus  Meek  and  Worthen,  Qeol.  Survey  111.,  vol.  3,  p 

528,  pi.  20,  agar.  7a-e. 
1S!»4.     l'nuhii  I  us  maijiius  Key  ox.  Mo.  (iool.  Surv.,  vol.  5,  p.  41. 

Descript ion. — Shell  Large,  subhemispherical  in  form,  broader  than  long, 
the  greatest  width  at  or  near  the  hinge-line.  The  dimensions  of  a  nearly 
complete  pedicle  valve  are:  length  from  hinge-lino  to  front  margin  60 
mm.,  length  from  unihoiial  region  to  front  margin  65  mm.,  greatest  width 
73  mm.,  convexity  43  mm. 

Pedicle  valve  gibbous,  arched  longitudinally  with  the  curvature 
usually  more  abrupt  posteriorly,  the  umbonal  region  depressed-convex, 
only  a  little  protuberant  beyond  the  hinge-line,  the  lateral  slopes  gently 
convex,  rather  broadly  sloping  from  the  central  portion  of  the  valve  to 
the  lateral  margins,  the  auriculations  at  the  cardinal  extremities  only 
slightly  differentiated  from  the  general  curvature  of  the  lateral  slopes; 
mesial  sinus  shallow,  rather  narrow,  rounded  in  the  bottom,  sometimes 
almost  obsolete ;  beak  small  and  strongly  incurved.  Surface  covered  with 
somewhat  obscure,  depressed,  rounded,  radiating  costae  which  are  rather 
slender  for  the  size  of  the  shell,  usually  about  1  mm.  from  center  to  center 
towards  the  front  of  the  valve,  they  continue  to  increase,  usually  by  bifur- 
cation through  the  entire  length  of  the  valve ;  more  or  less  indistinct, 
wrinkle-like,  concentric  markings  occur  upon  the  posterior  slope  of  the 
valve,  and  concentric  lines  of  growth  are  present  over  the  entire  surface. 
Rather  obscure  spine  bases  are  sparsely  scattered  over  the  shell  surface 
towards  the  anterior  and  lateral  margins,  and  a  group  of  stronger  and 
more  conspicuous  ones  occur  near  the  cardinal  margin,  these  cardinal 
spines  grow  larger  towards  the  cardinal  extremities  and  are  sometimes 
arranged  in  a  series  of  three  or  four  oblique  rows  with  from  two  to  five 
spines  in  each  row.  Interiorly  the  muscular  scars  are  rather  strongly 
developed  and  the  entire  inner  surface  is  roughened  by  rather  fine  pits, 
the  anterior  and  lateral  margins  which  are  in  contact  with  the  produced 
portion  of  the  opposite  valve  being  smoother  and  rather  sharply  differen- 
tiated from  the  visceral  portion. 

Brachial  valve  flattened  towards  the  beak  and  only  gently  concave 
through  the  entire  visceral  region,  curving  more  strongly  towards  the 
anterior  and  lateral  margins  but  not  geniculate,  the  auricular  portions 
towards  the  cardinal  extremities  not  differentiated  from  the  general  sur- 
face ;  the  mesial  portion  of  the  valve,  in  its  anterior  half,  slightly  ele- 
vated in  a  low  and  narrow  fold.  Surface  of  the  valve  marked  by  radiat- 
ing costaa  and  concentric  markings  similar  to  those  of  the  opposite  valve. 
Internally  the  large  and  strong  cardinal  process  is  bifid  at  its  extremity, 
anteriorly  from  its  base  a  low,  ridge-like  septum  extends  for  three-fourths 
or  more  of  the  length  of  the  valve,  and  a  cardinal  ridge  extends  laterally 
from  each  side  of  the  base  of  the  cardinal  process  nearly  parallel  with 
the  cardinal  margin;  the  brachial  impressions  are  often  distinctly  visible 


PRODUCTUS  119 

and  lie  anterior  to  the  middle  of  the  valve ;  subparallel  with  the  anterior 
and  lateral  margins  a  rugose  ridge  formed  by  the  thickening  of  the  inner 
surface  of  the  valve  differentiates  the  visceral  portions  from  the  portion 
which  is  produced  in  contact  with  the  opposite  valve. 

Remarks. — This  is  one  of  the  largest  of  our  species  of  Productus  and  is 
readily  distinguished  from  any  other  here  described  by  its  subhemispheri- 
cal  form,  its  slightly  protuberant  umbo  of  the  pedicle  valve,  its  broadly 
sloping  lateral  slopes  and  its  slightly  differentiated  auriculations.  The 
arrangement  of  spine  bases  in  oblique  rows  along  the  cardinal  margin,  as 
described,  has  been  clearly  observed  in  several  examples,  in  all  the  speci- 
mens studied  in  which  the  preservation  is  sufficiently  good  to  exhibit  the 
character  of  these  spines,  and  it  is  not  unlikely  that  this  arrangement  is 
characteristic  of  the  species.  The  shell  described  by  Swallow  as 
P.  fentonensis  is  clearly  identical  with  P.  magnus,  although  no  examples 
from  Fenton,  Missouri,  have  been  seen  which  are  as  large  as  the  larger 
examples  of  P.  magnus  from  Monroe  County,  Illinois,  the  type  locality  for 
the  species. 

Horizon. — Upper  Keokuk  limestone. 

Productus  tenuicostus  Hall 
Plate  X,  Figs.  25-27 ;  Plate  XI,  Figs.  1-5 

1858.     Productus  tenuicostus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  675,  pi.  24, 

figs.  2a-d. 
1883.     Productus  tenuicostus  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi. 

(18)  49,  fig.  18. 
1892.     Productus  tenuicostatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  18,  fig.  18. 
1894.     Productus  tenuicostus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  44. 

Description.  —  Shell  thin,  of  medium  size,  length  and  width  subequal  or 
longer  than  wide,  the  hinge-line  shorter  than  the  greatest  width.  The 
dimensions  of  an  incomplete  pedicle  valve  are :  length  from  hinge-line 
to  front  margin  ±25  mm.,  length  from  umbonal  region  to  front  margin 
±31  mm.,  greatest  width  ±28  mm.,  length  of  hinge-line  ±24  mm.,  con- 
vexity ±14  mm. 

Pedicle  valve  gibbous,  the  greatest  convexity  posterior  to  the  middle, 
the  umbonal  region  broad  and  protuberant  beyond  the  hinge-line,  the 
surface  gently  convex  transversely  or  slightly  sinuate  in  the  median  re- 
gion for  about  one-half  the  total  width  of  the  valve,  the  lateral  slopes 
curving  abruptly  to  the  lateral  margins  and  usually  a  little  inflected  to 
the  cardinal  margin,  the  anterior  slope  with  a  much  more  gentle  curva- 
ture, the  valve  sometimes  flaring  slightly  towards  the  lateral  and  anterior 
margins,  towards  the  cardinal  extremities  the  valve  is  compressed  some- 
what abruptly  to  form  rather  prominent  auriculations.  Surface  marked  by 
fine,  more  or  less  irregular,  rounded,  radiating  costaa  usually  about  one- 


120  M  Ississiitian    BRACHIOPODA 

half  millimeter  apart,  which  increase  somewhal  regularly  by  bifurcation 
and  intercalation  upon  the  posterior  slope,  often  becoming  more  or  less 
wavy  or  flexuose  upon  the  anterior  and  antero-lateral  slopes  and  increasing 
irregularly  by  intercalation  or  bifurcation,  or  sometimes  anastomosing; 
upon  the  posterior  slope  of  the  valve  there  are  rather  regular,  concentric, 
wrinkle-like  markings  which  vary  in  strength  upon  different  individuals 
and  usually  become  stronger  towards  the  cardinal  margins;  fine  concen- 
tric lines  of  growth  cover  the  entire  surface  when  it,  is  perfectly  pre 
served;  spine  bases  rare  or  wholly  absent  upon  the  body  of  the  valve,  but 

indications   of   a    small    group   of   spines   of   moderate   size   ..re    frequently 
present    upon   the  auricula!  ions  near  the  cardinal   margin. 

Brachial  valve  nol   observed. 

Remarks. — This   species    is   characterized    by    the    fine    radiating   costae 

and    by   the   thinness  of  the  shell   suhstanre.      To   this   last   character  may 

be  due  the  irregular  and  more  or  less  flexuous  growth  of  the  costae  upon 
the  anterior  and  lateral  slopes  of  the  valve  because  of  its  special  liability 
to  injury  during  growth.  The  flaring  of  the  pedicle  valve  towards  its 
outer  margin,  which  is  sometimes  present,  is  perhaps  due  to  deformation 
of  the  shell  during  fossilization,  again  because  of  its  delicacy.  In  some 
respects  the  members  of  this  species  resemble  P.  ovatus,  but  its  relation- 
ship is  rather  with  the  semireticulatus  type  of  the  genus  than  with  the 
i  nr,i  type,  because  of  the  much  more  continuous,  concentric,  wrinkle-like 
markings  of  the  posterior  slope  of  the  shell.  The  shell  resembles  P.  ovatus 
in  its  delicacy  and  in  its  tine,  more  or  less  flexuous  costae,  but  in  that 
species  and  its  allies  the  cross  wrinkles  are  confined  closely  to  that  portion 
of  the  valve  adjacent  to  the  cardinal  extremities. 
Ilorizon.  —  St.  Louis  limestone. 

Productus  scitulus  Meek  and  Worthen 
Plate  XIII,  Figs.  24-29 

1860.     Productus  scitulus  Meek  and  Worthen,  Proc.  Acad.  Nat.  Sci.  Phil., 

p.  451. 
1866      Productus  scitulus  Meek    and    Worthen,    Geol.    Surv.  111.,  vol.   2. 

p.  280.  pi.  20,  figs.  5a-d. 

Description.— Shell  small,  usually  broader  than  long  but  becoming  a 
little  longer  than  wide  in  old  individuals,  the  hinge-line  about  equaling 
the  greatest  width  of  the  shell,  the  anterior  margin  regularly  rounded. 
The  dimensions  of  a  large  and  old  example  are :  length  from  hinge-line 
to  front  margin  9.3  mm.,  length  from  umbonal  region  to  front  margin 
13.5  mm.,  greatest  width  13  mm.,  convexity  of  pedicle  valve  8.1  mm. 

Pedicle  valve  gibbous,  arched  from  the  umbonal  region  to  the  front 
with  the  posterior  curvature  shorter  and  a  little  more  abrupt  than  the 
anterior,  the  umbonal  region  strongly  protuberant  beyond  the  hinge-line. 


I'HODI    (II    S 


121 


the  median  portion  of  the  valve  gently  convex  transversely,  curving  more 
strongly  into  the  lateral  slopes  which  drop  more  or  less  abruptly  to  the 
Lateral  margins,  auriculations  at  the  cardinal  extremities  rather  sharply 
differentiated,  of  moderate  size,  rather  strongly  convex  antero-posteriorly  : 
the  median  sinus  usually  obsolete,  but  in  occasional  examples  a  slight. 
median  depression  occurs;  the  beak  strongly  incurved.  Surface  of  the 
valve  marked  by  fine,  radiating  costae,  about  three  of  which  occupy  the 
space  of  1  mm.,  they  increase  by  bifurcation  and  intercalation  on  the 
posterior  slope  of  the  valve  but  continue  with  few  or  no  divisions  across 
the  anterior  slope,  on  occasional  examples  several  groups  of  two  or  three 
eostas  arc  raised  slightly  above  the  general  surface  upon  the  anterior 
slope;  crossing  the  radiating  costae  upon  the  posterior,  slope  are  more  or 
less  well-defined,  concentric,  wrinkle-like  markings  which  are  commonly 
stronger  toward  the  cardinal  margin :  when  the  surface  is  not  exfoliated, 
minute,  concentric  lines  of  growth  are  present.  Spine  bases  are  commonly 
inconspicuous,  but  a  few  rather  widely  scattered  ones  are  sometimes 
present,  usually  upon  the  anterior  slope. 

Brachial  valve  not  observed. 

Remarks.— This  species  is  a  common  one  in  the  St.  Louis  limestone 
and  may  be  easily  recognized  by  its  small  size  and  its  fine,  radiating 
costae. 

Horizon.— St.  Louis  limestone. 

Productus  parvus  Meek  and  Worthen 
Plate  XVI,  Figs.  16-22 

1860.     Productus  parvus  Meek  and  Worthen,  Proc.  Acad.  Nat.  Sci.  Phil., 

p.  450. 
1866.     Product  us   parvus   Meek   and   Worthen,     Geol.     Surv.    111.,    vol.    2, 

p.  297,  pi.  23,  figs.  4a-e. 
1888.     Productus  parvus  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  4,  pi. 

11,  fig.  11. 
Description.  —  Shell  small,  length  and  width  usually  nearly  equal,  the 
greatest  width  near  the  mid-length  of  the  shell,  the  hinge-line  about 
equaling  the  greatest  width.  The  dimensions  of  a  nearly  perfect  specimen 
are:  length  from  umbonal  region  to  front  margin  14  mm.,  length  from 
hinge-line  to  front  margin  10.5  mm.,  greatest  width  14.8  mm.,  length  of 
hinge-line  14  mm.,  convexity  of  pedicle  valve  8.5  mm.,  depth  of  visceral 
cavity  between  the  two  valves  5.2  mm. 

Pedicle  valve  gibbous,  the  umbonal  region  broad  and  conspicuously 
protuberant  beyond  the  hinge-line,  mesial  portion  of  the  valve  from  the 
umbonal  region  to  the  front  broadly  flattened  or  gently  convex  trans- 
versely, the  surface  of  the  valve  arched  from  the  umbonal  region  to  the 
front  margin  with  the  top  of  the  arch  usually  situated  posterior  to  the 
middle,  the  lateral  slopes  curving  abruptly  to  the  margins,  the  auricula- 


122  MIssissilTl.w    BRACHIOPODA 

lions  at  the  cardinal  extremities  rather  small  and  somt'wlial  inflated;  the 
beak  strongly  incurved  beyond  the  binge-line;  the  mesial  sinus  absent 
or  very  slightly  developed.  Surface  of  the  valve  marked  by  fine,  rounded, 
radiating  costs,  aboul  four  of  which  occupy  the  space  of  two  millimeters 
towards  the  front  of  the  shell,  posteriorly  the  costue  increase  by  bifur- 
cation, bul  beyond  the  middle  of  the  valve  they  continue  to  the  front 
margin  cither  with  none  or  with  infrequent  divisions;  crossing  the 
radiating  costs  on  the  posterior  portion  of  the  valve  there  are  rather 
inconspicuous,  wrinkle-like,  concentric  markings  which  are  strongest 
near  the  anriculat ions ;  the  entire  surface  also  marked  by  extremely  line 
concentric  lines  of  growth  which  are  oil  en  obliterated  by  exfoliation 
of  the  surface.  Spine  bases  scattered  more  or  less  sparsely  over  the 
surface  of  the  valve  with  a  regularly  arranged  raw  usually  or  always 
present  upon  each  side  of  the  beak,  starting  close  to  the  hinge-line  and 
describing  a  curve  around  the  base  of  the  auriculation  to  the  lateral 
margin  a  short  distance  in  front,  of  the  cardinal  extremity,  the  spines 
continuously  becoming  stronger  distally.  Internal  characters  not  ob- 
served. 

Brachial  valve  deeply  and  rather  regularly  concave,  produced  ante- 
riorly and  laterally  nearly  in  contact  with  the  opposite  valve,  the  auricu- 
lar portions  at  the  cardinal  extremities  somewhat  differentiated  from  the 
general  surface.  Surface  marked  by  radiating  costai  similar  to  those  of 
the  opposite  valve  and  also  by  concentric  markings;  spine  bases  appar- 
ently infrequent  or  absent.     Internal  characters  not  observed. 

Hi  murks. — This  species  is  characterized  by  its  small  size,  its  broad  urn- 
bonal  region,  and  by  the  arrangement  of  the  spine  bases  in  a  row  around 
the  bases  of  the  auricular  extension  of  the  pedicle  valve.  The  typical 
form  of  the  species  occurs  in  the  Chester,  but  a  form  from  the  Pella  beds 
of  Iowa  has  also  been  referred  here,  which  shows  some  variation  from 
the  typical  form.  In  size,  general  form  and  proportions  the  two  shells 
are  essentially  alike  except  that  some  of  the  Pella  specimens  are  a  little 
larger.  The  chief  difference  lies  in  the  greater  number  of  spine  bases 
upon  the  Pella  examples  over  the  entire  surface  of  the  pedicle  valve,  and 
in  the  crowding  of  a  group  of  them  upon  the  auriculations  outside  of  the 
row  which  encircles  the  auriculation. 

Horizon. — Ste.  Genevieve  limestone  and  Chester  group. 

Productus  setigerus  HaJl 
Plate  XII,  Figs.  1-3 

1858.     Productus  setigerus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  638,  pi.  19, 

fig.  3. 
1883.     Productus  semireticulatm  Hall,  Rep.  N.  Y.  State  Geol.  for  1882. 
pi.  (18)  49,  fig.  13  (not  figs.  11  and  12). 


PRODUCTUS  123 

1892.     Producius  semireticulatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  18,  fig.  13  (not  figs.  11  and  12). 

Description.— Shell  above  medium  size,  about  as  long  as  wide,  the 
hinge-line  about  equaling  the  greatest  width.  The  dimensions  of  the 
holotype,  a  crushed  example  showing  only  the  brachial  valve  with  the 
ambonal  region  of  the  pedicle  valve,  are:  length  of  brachial  valve  30  mm., 
length  of  pedicle  valve  40  mm.,  greatest  width  40  mm.  The  dimensions 
of  a  somewhal  distorted  pedicle  valve  are:  length  from  front  to  hinge 
line  28  mm.,  length  from  front  to  greatest  extension  of  umbo  34..'5  mm., 
greatest  width  31  mm.,  convexity  15  mm. 

Pedicle  valve  gibbous,  the  anterior  slope  apparently  somewhat  more 
abrupt  than  the  posterior,  the  umbonal  region  narrow  and  strongly  pro- 
tuberant posteriorly,  the  mesial  portion  of  the  valve  broadly  flattened, 
the  lateral  slopes  curving  abruptly  to  the  margins,  the  cardinal  aurieula- 
tions  large,  flattened,  and  rather  abruptly  differentiated  from  the  lateral 
slopes ;  mesial  sinus  shallow,  rather  narrow,  and  ill-defined  laterally ; 
beak  pointed  and  strongly  incurved.  Surface  marked  by  rounded,  radiat- 
ing costs?,  usually  a  little  less  than  1  mm.  from  center  to  center,  increasing 
at  intervals  by  bifurcation ;  upon  the  posterolateral  slopes  and  extending 
across  the  cardinal  auriculations,  rather  strong,  concentric  wrinkles 
cross  the  radiating  costffl ;  very  flue  concentric  lines  of  growth  mark 
the  entire  surface  of  the  valve  when  it  is  perfectly  preserved.  Spine 
bases  are  scattered  rather  generally  over  the  surface  of  the  valve,  es- 
pecially over  the  median  and  anterior  regions,  usually  being  placed  at 
intervals  of  from  5  to  10  mm.  apart  upon  the  radiating  costas,  and  be- 
coming somewhat  more  numerous  upon  the  lateral  slopes  towards  the 
cardinal  extremities. 

Brachial  valve  apparently  gently  concave  or  somewhat  flattened  in 
the  visceral  region,  and  curving  abruptly  towards  the  anterior  and  lat- 
eral margins  into  the  produced  portion  of  the  valve ;  the  cardinal  auricu- 
lations rather  sharply  differentiated  from  the  general  surface  of  the 
valve.  Surface  marked  by  radiating  costte  similar  to  those  of  the  oppo- 
site valve,  and  also  by  similar,  fine  concentric  markings;  the  concentric 
wrinkles  of  the  shell  are  less  conspicuous  than  upon  the  pedicle  valve ; 
scattered  spine  bases  occur  about  as  in  the  opposite  valve,  increasing  in 
number  upon  the  cardinal  auriculations. 

Remarks. — This  species  is  evidently  a  rather  thin-shelled  form,  since 
the  specimens  observed  are  usually  more  or  less  distorted.  The  species 
has  not  been  commonly  recognized  since  its  original  definition,  and  has 
often  been  considered  as  a  synonym  of  P.  semireticulatus.  The  holotype 
of  the  species  is  a  crushed  example  upon  a  limestone  slab,  the  brachial 
valve  and  the  umbonal  region  only  of  the  pedicle  valve  being  exposed; 
extending  diagonally  outward  from  each  side  of  the  beak  is  a  crowded 


124  \i  ississi  I'l'l  an    BRACHIOPODA 

group    of   ratlin-    delicate    spines    which    originate    from    the    cardinal 

auricula  1  ions  of  the  pedicle  valve  and  attain  an  extreme  length  of  about 
30  mm.  The  specimen  described  by  Hall  as  /'.  srliijcrifs  var.  kcokuk  is 
fi  good  example  of  P.  rim nial is  White,  from  which  /'.  seiigcrus  differs 
in  its  smaller  size,  ils  finer  costs,  its  proportionally  more  elongate  hinge- 
line,  and  the  Larger  cardinal  auriculations.  In  some  respects,  especially  in 
its  relatively  fine  costs,  /'.  setigerus  suggests  P.  altonensis  of  the  Salem 
Limestone,  but  it  is  larger  than  that  species  with  relatively  larger  car- 
dinal auriculations  and  possesses  a  slight  median  sinus  in  the  pedicle 
valve. 
Horizon. — Keokuk  limestone. 

PrODUCTUS  ALTONENSIS  Norwood  and  Pratten 
Plate  X,  Figs.  14-24 

1855.     Productus  altonensis  Norwood  and  Pratten,  Jour.  Phil.  Acad.  Sci. 

(2),  vol.  3,  p.  7,  pi.  1,  figs.  la-c. 
1894.     Productus  altonensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  43. 
190(1.     Productus  burlingtonensis  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind., 

p.  1301,#pl.  17A,  figs.  1-lc. 
1906.     Productus  gallatinensis  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p. 

1302.  pi.  17 A,  figs.  2-2a. 

Description. — Shell  a  little  below  medium  size,  usually  a  little  wider  than 
long,  the  greatest  width  about  the  mid-length  of  the  shell,  the  hinge-line 
nearly  or  quite  equaling  the  greatest  width.  The  dimensions  of  a  pedicle 
valve  are :  length  from  hinge-line  to  front  margin  18  mm.,  length  from 
umbonal  region  to  front  margin  22.5  mm.,  width  24.2  mm.,  length  of 
hinge-line  ±24  mm.,  convexity  16  mm. 

Pedicle  valve  gibbous,  the  umbonal  region  conspicuously  protuberant 
beyond  the  hinge-line,  its  sides  converging  rather  rapidly  towards  the 
beak,  the  angle  of  convergence  often  being  less  than  90  degrees,  the 
surface  dropping  abruptly  to  the  cardinal  margin,  nearly  regularly 
arched  from  the  umbonal  region  to  the  front  margin,  curving  abruptly  to 
the  lateral  margins,  compressed  towards  the  cardinal  extremities  in  flat- 
tened auriculations  of  moderate  size ;  mesial  portion  of  the  valve  broadly 
flattened  with  the  flattened  region  illdefined  laterally,  mesial  sinus  com- 
monly obsolete,  when  present  it  is  very  slight ;  beak  pointed  and  strongly 
incurved.  Surface  of  the  valve  marked  by  rather  fine  radiating  plica- 
tions which  are  subangular  posteriorly,  becoming  more  rounded  an- 
teriorly, from  three  to  four  usually  occupy  the  space  of  2  mm.  in  front, 
in  the  posterior  portion  of  the  valve  the  costre  increase  frequently  by 
bifurcation,  but  anteriorly  they  continue  with  few  or  no  divisions  to  the 
front  margin ;  upon  the  lateral  slopes  of  the  valve,  adjacent  to  and 
upon  the   auriculations,   conspicuous,   wrinkle-like,   concentric  markings 


PRODUCTUS  125 

are  developed  which  are  either  obsolete  across  the  mesial  portion  of 
the  valve  or  are  much  reduced  in  strength;  the  entire  surface  of  the 
valve  marked  by  very  Hue.  bul  well-defined  concentric  markings;  when 
partially  exfoliated  the  shell  substance  is  seen  to  be  rather  coarsely 
but  closely  punctate,  the  punctations  being  more  closely  crowded  upon 
the  summits  of  the  costse  than  in  the  intercostal  furrows;  spine  bases 
apparently  absent  or  very  sparsely  present  upon  the  main  portion  of  the 
valve,  becoming  more  abundant  towards  the  anterior  and  lateral  margins, 
with  a  rather  closely  crowded  group  upon  each  auriculation.  Internal 
characters  not   observed. 

Brachial  valve  concave  throughout,  produced  anteriorly  nearly  in  con- 
tact with  the  opposite  valve,  the  auriculations  at  the  cardinal  extremities 
distinctly  differentiated,  the  visceral  cavity  between  the  two  valves 
rather  deep.  Surface  marked  by  radiating  costre  similar  to  those  of 
the  opposite  valve  but  somewhat  finer,  and  by  concentric,  wrinkle-like 
markings  which  are  somewhat  finer  but  more  uniformly  developed 
than  those  upon  the  posterior  portion  of  the  opposite  valve;  the  fine 
concentric  markings  similar  to  those  of  the  opposite  valve.  Spine  bases 
confined  chiefly  to  the  auriculations  and  along  the  hinge-line,  sparsely 
scattered  or  apparently  absent  from  other  portions  of  the  valve. 

Re  marks.  —  This  species  has  not  been  generally  recognized  since  its 
original  definition  by  Norwood  and  Pratten,  probably  because  of  the 
very  unsatisfactory  illustration  of  the  species  which  was  published  by 
those  authors.  The  shell  is  a  common  one  in  the  Salem  limestone  and 
has  been  identified  as  P.  burlingtonensis  and  P.  gallatinensis  by  'Beede. 
The  species  differs  from  P.  burlingtonensis  in  its  smaller  size,  its  finer 
costa^,  the  more  pointed  umbonal  region,  the  obsolescent  character  of 
the  concentric  wrinkle-like  markings  upon  the  median  portion  of  the 
posterior  part  of  the  pedicle  valve,  and  in  the  absence  of  a  median 
sinus  in  the  pedicle  valve.  In  the  strong,  concentric,  wrinkle-like  mark- 
ings of  the  shell  upon  and  adjacent  to  the  auriculations  and  their  nearly 
or  complete  absence  across  the  median  portion  of  the  pedicle  valve,  the 
species  resembles  P.  ovatus,  but  the  radiating  costa?  are  much  stronger  than 
in  that  species  and  they  lack  the  wavy  direction.  The  punctate  char- 
acter of  the  shell  in  this  species,  which  is  frequently  shown  in  partially 
exfoliated  specimens,  has  not  been  observed  in  any  other  species  here 
described. 

Horizon. — Salem  limestone. 


126  MISSISSIPPIAN    BEACHIOPODA 

PrODUCTUS  WOBTHBN]   Hall 

Plate  XIII.  Pigs.  1.5-17 

L858.     Products  wortheni  Hall,  Geol.  Iowa,  vol.  1,  pi.  2,  p.  f>:55,  pi.  ]!), 
figa.  la-b. 

Description,  Shell  of  medium  size  or  smaller,  usually  broader  than  long, 
i  In'  binge-line  about  equaling  the  greatesl  width.  The  dimensions  of  a 
nearly  complete  pedicle  valve  are:  Length  from  hinge-line  to  front 
margin  li»  mm.,  Length  from  umbonal  region  to  front  margin  21.4  mm., 
width  24  nun.,  convexity  15.5  nun. 

Pedicle  valve  gibbous,  the  umbonal  region  prominent  and  protuberant 
beyond  the  binge-line,  the  surface  curving  abruptly  towards  the  margins, 
depressed  at  the  cardinal  extremities  to  form  flattened  auriculations  of 
moderate  size,  along  Ihe  lateral  and  anterior  margins  a  slight,  inflated, 
ring  like  border  is  developed;  beak  pointed  and  slightly  incurved; 
mesial  sinus  obsolete,  although  the  mesial  portion  of  the  valve  is  some- 
times distinctly  flattened.  Surface  marked  by  rather  fine,  rounded  or 
subangular,  radiating  costae  which  increase  usually  by  bifurcation  on 
the  posterior  portion  of  the  valve,  and  usually  continue  across  the  an- 
terior slope  without  further  division,  becoming  more  or  less  discontinu- 
ous upon  flic  slightly  inflated  marginal  border;  about  three  costae  occupy 
the  space  of  two  millimeters  in  front,  becoming  finer  towards  the  car- 
dinal extremities;  the  posterior  portion  of  the  valve  is  crossed  also 
by  more  or  less  inconspicuous,  wrinkle-like,  concentric  markings  which 
become  stronger  towards  the  cardinal  extremities ;  spine  bases  occur 
rather  sparsely  scattered  upon  the  anterior  slope  of  the  valve,  becoming 
more  crowded  and  finer  upon  the  marginal  border,  a  group  of  rather 
closely  crowded  spine  bases  also  occupies  the  greater  portion  of  the 
surface  of  the  auriculations.  Internal  characters  of  the  valve  not 
observed. 

Brachial  valve  nearly  flat  through  the  greater  portion  of  its  area, 
becoming  abruptly  deflected  near  the  lateral  and  anterior  margins  and 
continuing  in  contact  with  the  opposite  valve,  the  flattened  portion  of  the 
valve  is  a  little  concave  at  the  beak  with  a  rather  broad  and  low  ill- 
defined  elevation  extending  obliquely  from  each  side  of  the  beak  towards 
the  lateral  margins,  outside  of  which  the  auriculations  are  not  sharply 
differentiated.  Surface,  of  the  valve  marked  by  radiating  costas  similar 
to  those  of  the  opposite  valve,  and  by  concentric,  wrinkle-like  markings 
which  are  more  conspicuous  than  those  of  the  opposite  valve ;  spine  bases 
are  rare  upon  the  greater  portion  of  the  surface,  but  become  abundant 
upon  the  deflected  marginal  border  and  upon  the  auriculations.  In- 
ternally the  cardinal  process  extends  posteriorly  from  the  hinge-line 
into  the  umbonal  cavity  of  the  opposite  valve ;  anteriorly  from  the  base 


PBODUCTUS  127 

of  the  cardinal  process  a  low  median  ridge  or  septum  reaches  beyond 
the  middle  of  the  valve. 

Remarks. — This  species  lias  its  nearest  ally  in  P.  marginicinctus  but  it 
differs  markedly  from  that  species  in  the  much  less  development  of 
the  inflated,  marginal  border  of  the  pedicle  valve,  in  the  finer  radiating 
eostse  and  the  less  conspicuous  concentric,  wrinkle-like  markings  of  the 
posterior  portion  of  the  shell,  and  in  the  absence  of  a  median  sinus  of 
the  pedicle  valve.  The  brachial  valves  are  more  nearly  alike,  both  being 
nearly  flat  throughout  most  of  their  width  and  length,  with  the  abruptly 
deflected  lateral  and  anterior  margins,  but  the  surface  markings  of  the 
valve  in  P.  wortht  ni  are  somewhat  finer  than  in  /'.  marginicinctus. 

Horizon. — Keokuk  limestone. 

Productus  marginicinctus  Pront 
Plate  XIII,  Figs.  18-23 

1857.  Productus  marginicinctus  Prout,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1. 

p.  43,  pi.  2,  figs.  1-16. 

1858.  Productus  marginicinctus  Hall,  Geol.  Iowa,  vol.  1.  pt.   2,  p.  674, 

pi.  24,  figs.  3a-d. 
1894.     Productus  marginicinctus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  43. 

Description.  —  Shell  below  medium  size,  usually  broader  than  long,  the 
hinge-line  shorter  than  the  greatest  width,  the  greatest  width  anterior 
to  the  mid-length  of  the  shell.  The  dimensions  of  a  specimen  of  average 
size  are :  length  from  hinge-line  to  anterior  margin  19.3  mm.,  length 
from  umbonal  region  to  anterior  margin  22  mm.,  width  24.5  mm.,  con- 
vexity of  pedicle  valve  15  mm.,  length  of  hinge-line  ±18  mm. 

Pedicle  valve  gibbous,  the  umbo  prominent  and  protuberant  beyond 
the  hinge-line,  the  surface  curving  abruptly  towards  the  margins,  com- 
pressed towards  the  cardinal  extremities  in  small  auriculations,  laterally 
and  anteriorly  the  surface  is  abruptly  deflected  near  the  margin  and  then 
convexly  curved  and  again  inflected  to  form  a  conspicuous,  ring-like  or  en- 
rolled border;  mesial  sinus  shallow  and  ill-defined,  sometimes  nearly  or 
quite  obsolete ;  beak  rather  small  and  pointed,  incurved.  Surface  of 
the  valve  marked  by  rather  strong,  rounded  costa3,  which  increase 
by  bifurcation  and  intercalation,  and  which  continue  with  only  slight 
interruption  across  the  ring-like  marginal  border;  on  the  anterior  por- 
tion of  adult  specimens  just  back  of  the  marginal  border  the  costas 
are  usually  about  one  millimeter  apart  from  center  to  center,  the  dis- 
tances varying,  however,  from  .5  to  1.5  mm.,  posteriorly  and  towards 
the  cardinal  extremities  the  eostae  are  finer;  at  more  or  less  irregular 
intervals  the  eostse  are  distinctly  nodose,  and  from  each  node  a  slender, 
elongate  spine  is  produced  anteriorly,  tangential  to  the  surface,  the 
spines   becoming   more   numerous   upon   the   marginal   border;    crossing 


128  MISSISSIPPI  \\    BRACHIOPODA 

the  radiating  costs  in  the  posterior  half  of  the  shell,  there  are  distinct, 
rounded,  wrinkle-like  concentric  markings,  which  are  stronger  towards 
the  cardinal  extremities,  and  the  entire  surface  is  covered   by  exceed 
ingly   fine,  concentric   markings,  which  are  stronger  in   the   intercostal 
furrows. 

Brachial  valve  nearly  Hal  throughoul  the  greater  portion  of  its  area, 

lull  curving  rather  abruptly  towards  the  lateral  and  anterior  margins 
and  continuing  for  a  short  distance  nearly  in  contact  with  tin;  inner 
surface  <>r  the  opposite  valve;  the  flattened  portion  of  the  valve  is 
gently  concave  towards  the  beak,  with  a  rather  broad,  slightly  elevated 
region  extending  obliquely  from  each  side  of  the  beak  to  the  lateral 
margins  a  little  in  front  of  the  cardinal  extremities,  the  auriculations 
flattened.  Surface  of  the  valve  marked  by  rounded,  radiating  COSte 
somewhat  more  depressed  than  those  of  the  opposite  valve,  which  in- 
crease by  bifurcation  and  intercalation;  the  costae  are  crossed  by  finer, 

r -enlric,  wrinkle-like  markings  which  give  to  nearly  the  entire  surface 

a  semireticulate  appearance,  and  also  by  much  finer  concentric  mark- 
ings similar  to  those  of  the  opposite  valve;  at  the  intersection  of  the 
stronger  radiating  and  concentric  markings,  especially  towards  the 
anterior  margin  of  the  valve,  are  slight  nodes  which  are  apparently  the 
bases  of  spines. 

Remarks.— This  is  one  of  the  most  distinct  species  of  the  genus 
Productus  in  our  faunas,  and  may  he  recognized  always  by  the  very  con- 
spicuous, ring-like  inflation  about  the  lateral  and  anterior  margins  of 
the  pedicle  valve.  The  only  other  species  among  those  here  recognized 
possessing  a  character  at  all  similar  to  this  one,  is  P.  wortheni,  but  in  P. 
marginicinctus  the  feature  is  very  much  more  conspicuously  developed. 
Both  these  species  are  peculiar  in  the  form  of  the  brachial  valve,  which 
is  so  nearly  flat  throughout  the  greater  portion  of  its  surface  with  the 
rather  abrupt  geniculation  near  the  lateral  and  anterior  margins. 

Horizon.— St.  Louis  limestone. 

Productus  parvulus  Winchell 

Plate  XIV,  Pigs.  24-25 

1863.     Producta  parvula  Winchell,  Proc.  Acad.  Nat,  Sei.  Phil.,  p.  4. 
1901.     Productus  parvulus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11,  p. 
160,  pi.  14,  figs.  21-22. 

Description.— Shell  very  small,  longer  than  wide,  the  hinge-line  equaling 
or  a  little  shorter  than  the  greatest  width.  The  dimensions  of  two  speci- 
mens, co-types,  are :  length  from  hinge-line  to  front  margin  8  mm.  and  6 
mm.,  length  from  umbonal  region  to  front  margin  9.1  mm.  and  6.9  mm., 
greatest  width  8.4  mm.  and  6.3  mm.,  length  of  hinge-line  8  mm.  and  6.3 
mm.,  convexity  5  mm.  and  3  mm. 


PRODUCTUS  129 

Pedicle  valve  strongly  convex,  the  umbonal  region  rather  narrow  and 
conspicuously  pro!  uberanl  beyond  the  hinge-line,  the  surface  curving 
abruptly  to  the  cardinal  margin,  compressed  towards  the  cardinal  ex- 
tremities to  form  small  hut  distinct  auriculatious,  to  the  lateral  and  an- 
terior margins  the  curvature  is  more  gentle;  mesial  sinus  absent;  the 
beak  small,  pointed  and  strongly  incurved.  Surface  of  the  valve  marked 
by  fine,  regular,  rounded  costae,  from  two  to  three  of  which  occupy  the 
space  of  one  millimeter,  all  concentric  markings  inconspicuous  or 
wanting. 

Brachial  valve  not  seen. 

Hi  marks.  —  The  specimens  which  have  been  used  for  the  basis  of  the 
above  description  are  Winchell's  co-types  from  the  upper  yellow  sand- 
stone of  the  Kindcrhook  at  Burlington,  Iowa.  The  specimens  are  in  the 
condition  of  internal  easts  and  do  not  preserve  the  markings  of  the  pos- 
terior portion  of  the  shell.  In  the  lower  beds  of  the  Burlington  lime- 
si  one  a  small  species  of  Productus  occurs  not  infrequently,  which  is  be- 
lieved to  represent  this  same  species,  although  it  grows  somewhat  larger 
than  the  types,  often  attaining  a  length  of  12  mm.  or  more.  These  speci- 
mens exhibit  the  surface  markings  better  than  the  types,  and  the  rounded 
costae  are  seen  to  become  nearly  or  quite  obsolete  before  they  reach  the 
apex  of  the  beak,  they  increase  by  bifurcation  at  intervals  and  bear  the 
bases  of  spines  which  exhibit  the  tendency  to  be  arranged  in  more  or  less 
definite  rows.  Distinct  concentric  wrinkles  are  absent  but  more  or  less 
regular  lines  of  growth  are  present,  in  addition  to  which  there  are  ex- 
ceedingly fine  concentric  stria\  The  impressions  of  the  brachial  valve  of 
the  Burlington  specimens  are  similar  in  general  form  to  the  pedicle  valve 
except  that  they  are  much  less  convex,  and  the  apical  portion  of  the  im- 
pression is  only  slightly  protuberant  beyond  the  hinge-line.  The  essen- 
tial characters  of  the  species  seem  to  be  the  small  size,  the  absence  of  a 
median  sinus  or  fold,  the  small  auriculations,  and  the  nature  of  the  sur- 
face markings. 

Horizon. — Upper    Kindcrhook   and   lower   Burlington   limestone. 

Productus  sampsoni  Weller 

Plate  XIII,  Figs.  30-35 

1909.     Productus  sampsoni  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  300, 
pi.  12,  figs.  18-22. 

Description.  —  Shell  small,  usually  longer  than  wide,  regularly  rounded 
or  somewhat  pointed  in  front,  the  hinge-line  shorter  than  the  greatest 
width,  the  cardinal  extremities  subangular  or  a  little  rounded.  The  di- 
mensions of  a  nearly  perfect  specimen  are:  length  from  hinge-line  to 
front  margin  8  mm.,  length  from  umbonal  region  of  pedicle  valve  to  front 

—5 


130  MississiriMAN    BRACHIOPOUA 

margin  10  mm.,  greatesl  width  9  nun.,  length  of  binge-line  7.5  mm.,  con- 
vexity of  pedicle  valve  4.5  nun.,  depth  of  visceral  cavity  between  the  two 
valves  1  .(i  mm. 

Pedicle  valve  strongly  convex  with  the  umbonal  region  prominent  and 
projecting  notably  beyond  the  binge  Line,  arched  longitudinally  with  the 

posterior   curvature   a    little  shorter  and    more   abrupt    than    the   anterior, 

the  lateral  slopes  curving  more  or  less  gently  from  the  rather  narrowly 
rounded  median  portion  of  the  valve  to  the  lateral  margins,  the  surface 
curving  abruptly  to  the  cardinal  margin,  cardinal  auriculations  small 
and  inconspicuous  or  obsolete;  mesial  sinus  obsolete;  beak  small,  pointed, 
and  strongly  incurved  beyond  the  binge-line.  Surface  of  the  valve 
marked  by  depressed,  rounded,  radiating  costse  which  are  broader  than  the 
intercostal  furrows,  from  one  and  one-half  to  three  of  which  occupy  the 
space  of  one  millimeter,  the  costse  increase  by  bifurcation  throughout  the 
entire  length  of  the  valve  but-  the  divisions  are  more  frequent  posteriorly; 
crossing  the  radiating  cost;e  are  i • •  less  irregular,  appressed,  concen- 
tric Laminae  which  in  some  conditions  of  preservation  of  the  shell  are  very 
conspicuous.  Spine  bases  \\'\v  and  inconspicuous,  sometimes  apparently 
obsolete,  when  present  they  are  usually  confined  to  about  two  or  three 
upon  each  side  of  the  beak  arranged  in  an  oblique  row  from  the  hinge- 
line  on  each  side  of  the  beak  towards  a  point  on  the  lateral  margin  in 
front  of  the  cardinal  extremity. 

Brachial  valve  deeply  concave,  closely  following  the  curvature  of  the 
pedicle  valve,  not  differentiated  into  a  visceral  and  a  produced  portion, 
the  surface  slightly  deflected  towards  the  cardinal  extremities.  Surface 
marked  by  radiating  costie  similar  to  those  of  the  opposite  valve,  and 
also  by  similar  concentric  lamina'. 

Remarks. — This  small  species  is  entirely  different  from  any  other  mem- 
ber of  the  genus  in  our  faunas.  It  resembles  in  a  somewhat  remote  de- 
gree the  Productella  halliana  of  the  Lime  Creek  Devonian  fauna  of  Iowa, 
but  it  is  commonly  a  narrower  shell,  more  prominent  along  the  median 
line  of  the  pedicle  valve  and  with  similar  markings  upon  the  two  valves. 

Horizon. — Chouteau  limestone,  and  Fern  Glen  formation. 

Productus  curtirostris  Winchell 

Plate  XIV,  Figs.  8-13 

1865.     Producta  curtirostra  "Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  114. 
1900.     Productus  semi  ret  ic  idatus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol. 
10,  p.  70,  pi.  1,  figs.  7-8. 

Description.— Shell  semielliptical  or  subsemielliptical  in  outline,  of  about 
medium  size  or  a  little  larger,  length  and  breadth  subequal,  the  hinge- 
line  equal  to  or  a  little  shorter  than  the  greatest  width.  The  dimensions 
of  two  nearly  complete  pedicle  valves,  co-types,  are :  length  from  hinge- 
line  to  anterior  margin  24.5  mm.  and  25.2  mm.,  length  from  umbonal  re- 


PRODUCTUS  131 

gion  to  front  margin  25  mm.  and  25.8  mm.,  greatest  width  30.8  mm.  and 
27.7  mm.,  length  of  hinge-line  26  mm.  and  26  mm.,  convexity  10  mm.  and 
9  mm. 

Pedicle  valve  convex  with  the  greatest  depth  posterior  to  the  middle, 
the  umhonal  region  very  slightly  protuberant  beyond  the  hinge-line,  the 
surface  of  the  valve  curving  rather  abruptly  to  the  cardinal  margin,  with 
the  curvature  only  slightly  modified  towards  the  cardinal  extremities  be- 
cause of  the  almost  obsolete  cardinal  auriculations,  to  the  lateral  and  an- 
terior margins  the  curvature  is  more  gentle;  mesial  sinus  entirely  want- 
ing; the  beak  very  short  and  obtuse,  scarcely  differentiated  from  the  um- 
bonal  surface  and  not  extended  beyond  the  cardinal  margin.  Surface  of 
the  valve  marked  by  low,  rounded,  moderately  fine,  more  or  less  discon- 
tinuous, longitudinal  eostse,  and  by  a  few  more  or  less  inconspicuous  con- 
centric wrinkles  posteriorly,  which  are  strongest  towards  the  cardinal 
extremities. 

Brachial  valve  concave,  the  curvature  following  that  of  the  pedicle 
valve  with  a  rather  thin  visceral  cavity,  with  no  mesial  fold  or  sinus.  The 
surface  markings  entirely  similar  to  those  of  the  opposite  valve. 

Rt  marks. — This  species  is  especially  characterized  by  the  flattened 
umbonal  region,  the  almost  obsolete  beak,  and  the  slight  posterior  pro- 
tuberance of  the  umbo.  In  its  general  aspect  the  form  of  the  pedicle 
valve  suggests  an  impression  of  the  concave  brachial  valve  of  some  species 
of  Productus,  and  for  a  time  the  species  was  so  interpreted.  A  sufficient 
number  of  examples  having  both  valves  in  place  have  been  observed,  how- 
ever, to  make  it  certain  that  such  an  interpretation  is  an  incorrect  one. 
and  that  Winchell  was  right  in  his  interpretation  of  the  species.  The  dis- 
continuity of  the  radiating  markings  of  the  shell,  together  with  the  low 
convexity  of  the  pedicle  valve,  are  somewhat  suggestive  of  the  genus 
Productella,  but  until  the  generic  characters  can  be  more  deefinitely  de- 
termined the  species  may  be  allowed  to  remain  in  Productus  where  it  was 
originally  placed  by  Winchell. 

Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 

Productus  indianensis  Hall 
Plate  XVIII,  Figs.  7-10;  Plate  LXXXIII,  Figs.  12-13 

1856.     Productus  Indianensis  Hall,  Trans.   Albany  Inst.,  vol.   1,  p.  47. 

1882.  Productus  Indianensis  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

p.  47,  pi.  6,  figs.  6-7. 

1883.  Productus  Indianensis  Hall,    12th   Hep.   Geol.   Surv.   Ind.,   p.   326, 

pi.  29,  figs.  6-7. 
1906.     Productus  indianensis  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p. 
1300,  pi.  19,  figs.  7-7a ;  pi.  22,  figs.  6-7. 

Description. — Shell  very  small,  longer  than  wide,  the  hinge-line  a  little 
shorter  than  the  greatest  width,  the  greatest  width  near  the  mid-length 


132  MISSISSIIT1AN    BRACHIOPOD.A 

The  dimensions  of  two  nearly  complete  pedicle  valves,  the  firsl  of  which 
is  .Hie  of  the  co-types,  are:  Length  from  hinge-line  to  front  margin  6.3  mm. 
ami  5.5  nun.,  Length  from  umbonal  region  to  front  margin  7.2  mm.  and 
(i..-)  nun.,  greatesl  width  6.9  nun.  and  ft.,")  mm.,  Length  of  hinge-line  5.6  mm. 
and  5  mm.,  im.h \ vxily  4  mm.  and  3.5  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  limbonal  region  broad  and  prominent,  strongly  protuberant 
beyond  the  binge-line,  the  surface  rather  narrowly  rounded  transversely 
along  the  median  line  of  the  valve,  curving  rather  abruptly  to  the  lateral 
margins  and  more  gently  to  the  anterior  margin,  a  little  compressed 
Inward  the  cardinal  extremities,  the  auricular  extensions  inconspicuous; 
mesial  sinus  obsolete;  beak  strongly  incurved  and  extending  beyond  the 
binge-line.  Surface  without  regular  radiating  costse,  but  marked  by  fine, 
concentric  lines  of  growth  which  are  somewhat  more  prominent  at  inter- 
vals, giving  a  rather  indefinite  concentrically  banded  appearance.  Spine 
bases  of  moderate  size  with  a  tendency  to  be  arranged  in  somewhat  irreg- 
ular concentric   rows. 

Brachial  valve  not  observed. 

Remarks.— The  original  illustrations  of  this  species  suggest  a  shell 
similar  to  /'.  biseriatus,  but  in  fact  the  two  species  are  entirely  different. 
/'.  indiam  nsis  is  much  smaller  than  /'.  biseriatus,  narrower,  more  strongly 
convex,  and  with  a  much  more  prominent  umbonal  region  in  the  pedicle 
valve.  The  surface  markings  of  the  two  shells  are  also  very  different, 
the  spines  of  /'.  indium  nsis  are  apparently  not  the  fine,  closely  appressed 
spines  of  P.  biseriatus  and  P.  punctatvs,  but  are  more  erect,  and  the  shell 
does  not  exhibit  the  distinctly  banded  markings  of  P.  biseriatus.  The 
style  of  ornamentation  with  the  absence  of  radiating  costas  and  somewhat 
indefinitely  arranged  spine  bases  suggests  some  of  the  shells  from  the 
Devonian  and  lower  Mississippian  faunas  which  have  usually  heen  re- 
ferred to  the  genus  Productclla,  and  it  is  possible  that  this  species  should 
be  so  referred. 

Horizon.  —  Salem  limestone. 

Productus  ovatus  Hall 
Plate  XVI,  Figs.  1-15 

1858.  Productus  ovatus  Hall  Geol.  Iowa,  vol.  1,  pt.  2,  p.  674,  pi.  24,  fig.  1. 

1859.  Productus  piriformis  McChesney,  Desc.  New  Pal.  Foss.,  p.  40. 

1860.  Productus  la'vicostus  White,  Jour.  Boston  Soc.  Nat.  Hist.,  vol.  7, 

p.   230. 
1863.     Productus  coroeformis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2, 

p.  94. 
1874.     Productus  prattcnianus   (=    ?  P.  kevicostus)   White,  Prelim.   Rep. 

Inv.  Foss.,  p.  17. 
1877.     Productus  prattenianus  (pars.)  White,  IT.  S.  Geog.  Surveys  W.  100th 

Mer.,  vol.  4,  p.  113. 


PRODUCTUS  133 

1877.    Product  us  Icevicostus  t  Hal]  and  Whitfield,  U.  S.  Geol.  Expl.  40th 

Par.,  vol.  4,  p.  266,  pi.  5,  figs.  7-8. 
1883.     Praductus  ovatus  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.   (18) 

49,  fig.  19. 

1891.  Praductus   pilciformis  Whitfield.    Ann.    N.    Y.    Acad.    Sci.,    vol.    5, 

p.  582,  pi.  13,  figs.  13-14. 

1892.  Product  us  oral  us  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  18, 

fig.  19. 
1894.     Product  us  Icevicostus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  41,  pi.  38, 
fig.  1. 

1894.  Prodmctus  ovatus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  44. 

1895.  Productus  pilciformis  Whitfield,  Geol.  Surv.  Ohio,  vol.   7,  p.  470, 

pi.  9.  figs.  13-14. 

1899.  Praductus  Icevicosta  Girty,  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p.  534, 

pi.  69,  figs.  9a-c. 

1900.  Productus  Icevicostus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  71,  pi.  1,  figs.  1-2. 
1903.     Productus  Icevicostus  Girty,  Prof.  Paper,  U.  S.  Geol.  Survey,  No.  16, 

p.  284. 
1909.     Productus  pileiformis   Girty,   Bull.   U.   S.   Geol.    Survev  No.   377, 

p.  26,  pi.  2,  fig.  7. 
1911.     Productus  pileiformis  Girtv,  Bull.  U.  S.  Geol.  Survey  No.  439,  p.  44, 

pi.  4,  figs.  1-2. 
1911.     Productus  pilciformis  Morse,  Proc.  Ohio  State  Acad.  Sci.,  vol.  5,  p. 

370,  figs.  8a-c. 

Description. — Shell  thin  and  delicate,  variable  in  size  but  usually  of 
medium  size  or  larger,  longer  than  wide,  the  hinge-line  shorter  than  the 
greatest  width,  the  cardinal  extremities  angular.  The  dimensions  of  a 
nearly  complete  pedicle  valve  are :  length  from  hinge-line  to  front  margin 
-j-27.5  mm.,  length  from  umbonal  region  to  front  margin  -4-34  mm.,  great- 
est width  27  mm.,  length  of  hinge-line  23.5  mm.,  convexity  22.5  mm. 

Pedicle  valve  gibbous,  the  greatest  convexity  posterior  to  the  middle, 
the  umbonal  region  prominent  and  strongly  protuberant  beyond  the 
hinge-line,  the  surface  arched  from  the  umbonal  region  to  the  front  with 
the  posterior  curvature  shorter  and  somewhat  more  abrupt,  the  lateral 
slopes  curving  abruptly  from  the  median  portion  of  the  valve  to  the  lat- 
eral margins,  and  deflected  as  they  approach  the  cardinal  extremities  to 
form  rather  small  auriculations ;  mesial  sinus  entirely  absent;  the  beak 
small,  pointed,  and  closely  incurved.  Surface  marked  by  fine,  rounded, 
radiating,  more  or  less  flexuous  costa?,  on  the  posterior  portion  of  the 
valve  they  are  more  regular  and  increase  frequently  by  intercalation,  the 
intercalated  costaa  increasing  in  size  very  gradually,  anteriorly  the  inter- 
calated eostse  becomes  less  frequent,  the  costa;  often  become  more  irregu- 
lar in  growth  and  more  flexuous  upon  the  more  mature  portion  of  the 
valve  where  from  two  to  three  costae  usually  occupy  the  space  of  one 
millimeter ;  towards  the  cardinal  extremities  and  extending  up  on  the 
lateral  slopes  there  are  strong  and  distinct,  rounded,  transverse  wrinkle- 


134  MISSISSIPPIAN    BRACHIOPODA 

like  folds  which  rarely  or  never  cross  tlio  median  portion  of  the  valve; 
the  rutin'  surface,  when  w.l  I  preserved,  marked  by  exceedingly  fine,  con 
centric    lines  of  growth.     Spine   bases   usually    inconspicuous,  but  rather 
elongate;  slender,  sparsely  scattered  spines  are  present  upon  some  speci- 
mens when   they  occur  in   ;i    favorable  condition  of  preservation. 

Brachial  valve  deeply  concave  with  the  surface  compressed  towards  the 
cardinal  extremities  to  form  small  auriculations,  the  convex  external  im- 
pressions of  the  valve  resemble  examples  of  the  pedicle  valve  except  that 
the  umbonal  region  protrudes  beyond  the  hinge-line  either  not  at  all  or 
only  slightly.  Surface  of  the  valve  marked  by  tine,  rounded,  more  or 
less  tlexuous  and  irregular,  radiating  COStfB,  entirely  similar  to  those  of 
the  opposite  valve;  towards  the  cardinal  extremities  strong,  concentric, 
wrinkle-like  folds,  similar  to  those  of  the  opposite  valve,  occur,  but,  un- 
like those  of  that  valve,  at  least  some  of  them  continue  across  the  median 
portion  of  the  valve,  although  much  more  faintly  developed  than  towards 
the  cardinal  extremities;  entire  surface,  when  well  preserved,  covered  by 
fine,  concentric,  lines  of  growth. 

Remarks.— This  species  ranges  through  the  Mississippian  formations, 
although  it  occurs  much  more  abundantly  at  certain  horizons  than  others. 
It  is  a  species  belonging  to  the  /'.  cora  group  of  the  genus,  and  should 
perhaps  not  be  considered  as  distinct  from  that  species.  On  comparison 
with  the  figures  of  the  type  specimen  of  P.  cora1  there  seems  to  be  no 
essential  features  which  can  be  used  to  distinguish  our  Mississippian 
shells,  unless  it  be  that  the  type  is  less  strongly  convex  transversely.  The 
auriculations  arc  imperfectly  preserved  in  D'Orbigny's  type,  and  do  not 
show  in  the  recent  illustration,  but  in  his  original  figure  they  are  made 
very  large  and  conspicuous  besides  being  mentioned  in  his  original  de- 
scription, and  they  may  have  been  destroyed  since  the  original  definition 
of  the  species  was  written.  These  Mississippian  shells  resemble  a  common 
form  in  the  Pennsylvanian  faunas  which  is  generally  more  broadly 
rounded  transversely  and  has  more  conspicuous  auriculations,  agreeing  in 
both  these  characters  with  the  original  P.  cora  with  which  they  are  com- 
monly identified,  and  as  the  Mississippian  and  Pennsylvanian  forms  are 
quite  certainly  distinct  specifically,  D'Orbigny's  name  is  retained  for  the 
later  form. 

Hall  described  P.  ovatus  in  1858  from  a  St.  Louis  limestone  specimen 
preserved  in  a  somewhat  weathered  condition.  The  type  specimen  does 
not  show  the  hinge-line,  but  it  does  show  the  surface  spines  more  satis- 
factorily than  most  examples.  In  the  more  recent  collections  many  speci- 
mens from  the  same  horizon  occur,  some  in  a  condition  of  preservation 
similar  to  the  type  and  others  showing  the  entire  form  of  the  shell  much 
more  satisfactorily,  and  it  is  from  such  examples  that  the  above  descrip- 

lPal.  Universalis,  vol.  1,  No.  2  (1903). 


DIAPIIRAGMUS  135 

tion  of  the  species  has  been  largely  made.  In  1859  McChesney  described 
his  P.  pileiformis  from  the  Chester  limestone,  and  while  examples  of  the 
species  are  less  common  in  this  horizon  than  in  the  St.  Louis  limestone,  a 
careful  examination  of  all  available  specimens  has  not  shown  a  single 
character  by  which  they  can  be  distinguished.  In  the  final  publication 
of  his  paper  in  1867,  McChesney1  gives  no  illustration  of  the  species  and 
makes  no  mention  of  it,  and  the  supposition  is  that  he  himself  abandoned 
it.  The  specimen  figured  by  Whitfield  under  this  specific  name  in  1891 
and  1895,  is  an  impression  of  the  exterior  of  the  brachial  valve  and  differs 
in  no  essential  respects  from  similar  specimens  of  P.  ovatus.  White's 
species  P.  twvicostus  was  described  in  1860  from  a  much  lower  horizon, 
the  Kinderhook,  and  his  type  specimens  have  never  been  illustrated. 
Authentic  specimens  from  the  typical  locality  are  at  hand,  however,  and 
no  way  has  been  discovered  by  which  they  can  be  distinguished  from  the 
specimens  from  the  higher  beds.  The  P.  corceformis  of  Swallow 
has  never  been  illustrated,  it  has  never  been  recognized  since  its  original 
definition  and  was  evidently  based  upon  a  small  example  of  the  common 
species  of  our  Mississippian  faunas. 

From  a  careful  examination  of  all  available  material  it  has  been  im- 
possible to  detect  means  of  differentiating  more  than  a  single  species  of 
Productus  of  the  type  of  P.  com  in  the  Mississippian  faunas  under  con- 
sideration, and  for  this  species  Hall's  name,  P.  ovatus,  has  priority.  The 
species  is  a  variable  one,  variations  in  proportional  length  and  breadth, 
coarseness  of  cost*,  strength  of  the  concentric,  wrinkle-like  folds,  and  in 
the  surface  spines  being  common,  but  in  no  case  have  the  variations  been 
found  to  be  constant  in  character. 

Horizon.— Kinderhook,  Burlington  limestone,  Keokuk  limestone,  Salem 
limestone.  St.  Louis  limestone,  Ste.  Genevieve  limestone,  and  Chester 
group. 

Genus  DIAPHRAGMUS  Girty 

Description. — Shell  productoid  in  form,  with  the  external  surface  of  the 
valves  marked  by  distinct  radial  cost*.  Internally  the  hinge  characters 
of  both  valves  resemble  Productus.  The  diagnostic  character  of  the 
genus  consists  of  a  partition  which  is  an  outgrowth  from  the  inner  surface 
of  the  brachial  valve  at  its  geniculation,  continuing  in  nearly  the  same 
plane  as  the  visceral  portion  of  the  valve  to  the  inner  surface  of  the 
pedicle  valve.  Beyond  this  partition  both  valves  are  notably  produced, 
their  inner  surfaces  being  nearly  or  quite  in  contact.  In  the  fossil  speci- 
mens the  visceral  surface  of  the  brachial  valve  continued  into  the  par- 
tition constitutes  a  cleavage  plane  along  which  the  shells  are  often 
broken. 

l  Trans.  Chicago  Acad.  Sci.,  vol.  1  (1867). 


136  MISSISSIPPIAN    BRACHIOPODA 

Remarks.  Among  the  productoid  genera  Diapkragmus  has  its  closest 
relative  in  Margimfera.  In  Margimfera,  however,  the  visceral  portion  of 
the  brachial  valve  is  surrounded  by  a  ridge-like  elevation  which  rises 
vertically  from  the  inner  surface  of  the  valve  instead  of  continuing  in 
the  .same  plane  as  is  the  condition  m  Diapkragmus.  Margimfera  has 
no1  as  yei  been  recognized  in  any  of  the  Mississippian  faunas,  its  earliest 
appearance  being  in  the  Pennsylvanian,  while  Diapkragmus  occurs  only 
in  the  Later  Mississippian,  so  far  as  it  is  known  at  present,  and  is  rep- 
resented by  a  single  species. 

Diaphbagmus  elegans  (Norwood  and  Pratten) 
Plate  XII,  KiKs.  8-17 

1855.     Productus   elegans    Norwood   and    Pratten,   Jour.    Acad.   Nat.   Sci. 

Phil.  c_M,  vol.  3,  ]>.  3,  pi.  1.  figs.  7a-c. 
1855.     Productus  flexistria  Norwood  and   Pratten,  Jour.   Acad.  Nat.  Sci. 

Phil.  (2),  vol.  3,  p.  (i. 
L860.     Productus  fasciculatus  McChesney,  Desc.  New  Pal.  Foss.,  p.  38. 
I860.     Productus  Cestriensis  Wbrthen,  Trans.  St.  Louis  Acad.  Sci.    vol.  1, 

p.  570. 
1877.     Productus  elegans  Hall  and  Whitfield,  U.  S.  Geol.  Expl.  40th  Par, 

vol.  4,  p.  268,  pi.  5,  figs.  3,  4. 
1891.     Productus  elegans  Whitfield,  Ann.  N.  Y.  Acad.  Sci.,  vol.  5,  p.  581, 

Pi.  13,  figs.  15,  16. 

1894.  Productus  cestriensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  44. 

1895.  Productus  <I<<i<ihs  Whitfield,  Geol.  Surv.  Ohio,  vol.  7,  p.  669,  pi.  !) 

figs.  15,  16. 
1897.     Productus  c<  strii  nsis  Weller,  Trans.  Nl  Y.  Acad.  Sci.,  vol.  16,  p. 
256,  pi.  18,  figs.  7-9. 

1909.  Productus  fasciculatus  Bassler,  Va.  Geol.  Surv.,   Bull.  No.   II  A, 

pi.  29,  figs.  12,  13. 

1910.  Diapkragmus  elegans  Girty,  Ann.  N.  Y.  Acad.  Sci.,  vol.  20,  p.  217. 

1911.  Diapkragmus  elegans  Girty,  Bull.  U.  S.  Geol.  Survey  No.  439,  p.  51, 

pi.  4,  figs.  4-5 
1911.     Productus  cestriensis  Morse,  Proc.  Ohio  State  Acad.   Sci.,  vol.  5, 
p.  372,  figs.  9a-g. 

Description. — Shell  usually  below  medium  size,  longer  than  wide,  the 
greatest  width  near  the  mid-length,  the  hinge-line  shorter  than  the  great- 
est width.  The  dimensions  of  a  pedicle  valve  of  about  average  size  are : 
length  from  hinge-line  to  front  margin  17  mm.,  length  from  umbonal  re- 
gion to  front  margin  22  mm.,  greatest  width  21.8  mm.,  length  of  hinge- 
line  17  mm.,  convexity  of  pedicle  valve  14  mm. 

Pedicle  valve  gibbous,  the  umbonal  region  protuberant  posteriorly  be- 
yond the  cardinal  margin,  the  surface  dropping  nearly  vertically  to  the 
cardinal  margins,  curving  abruptly  to  the  lateral  and  anterior  margins, 
compressed  at  the  cardinal  extremities  into  rather  small,  flattened  auricu- 
lations ;  mesial  portion  of  the  valve  usually  broadly  flattened  from  the 


DIAPHRAGMUS  137 

iimboiial  region  to  the  anterior  margin,  the  mesial  sinus  obsolete  or  very 
shallow  and  ill-defined ;  the  beak  strongly  incurved.  Surface  of  the  valve 
marked  by  rounded,  radiating  costae  which  increase  usually  by  bifurca- 
tion in  the  posterior  portion  of  the  valve,  and  continue  to  the  front  margin 
with  much  less  frequent  divisions,  in  some  specimens  becoming  more  or 
less  fasciculate  towards  the  front,  at  the  front  of  mature  shells  the  costae 
are  usually  separated  about  one  millimeter  or  less  from  center  to  center, 
becoming  somewhat  smaller  upon  the  lateral  slopes  towards  the  cardinal 
extremities ;  crossing  the  radiating  plications  upon  the  posterior  portion 
of  the  valve  are  rather  inconspicuous,  concentric,  wrinkle-like  markings 
which  are  often  nearly  obsolete,  other  exceedingly  fine  concentric  mark- 
ings cover  the  entire  surface  of  the  valve  when  it  is  well  preserved ;  spine 
bases  are  rare  or  nearly  obsolete  upon  the  greater  portion  of  the  surface 
of  the  valve,  those  present  being  sparsely  scattered,  usually  towards  the 
front,  but  upon  the  auriculations  and  the  lateral  slopes  just  inside  the 
auriculations,  is  a  group  of  rather  fine,  crowded  spine  bases,  sometimes 
forty  or  more  in  number. 

Brachial  valve  gently  concave  or  flattened  in  the  visceral  region, 
curving  more  strongly  anteriorly  and  laterally  where  the  outer  margin 
of  the  valve  is  conspicuously  produced  nearly  in  contact  with  the  inner 
surface  of  the  opposite  valve,  not  infrequently  the  inner  portion  of  the 
gently  concave  visceral  part  of  the  valve  is  more  or  less  differentiated, 
the  differentiated  region  being  somewhat  more  concave  and  being  bound- 
ed by  a  rather  strong,  concentric  line  of  growth.  Surface  of  the  valve 
marked  by  radiating  costfe  similar  to  those  of  the  opposite  valve,  often 
being  somewhat  better  defined  posteriorly  in  the  more  concave  differ- 
entiated portion  of  the  valve ;  ill-defined,  concentric,  wrinkle-like  mark- 
ings, usually  stronger  than  those  of  the  opposite  valve,  occupy  the  visceral 
portion  of  the  valve  and  the  entire  surface  is  covered  by  very  fine  con- 
centric markings  similar  to  those  of  the  opposite  valve ;  spine  bases 
commonly  if  not  always  absent.  Internally  the  posterior  visceral  portion 
of  the  valve  is  sharply  differentiated  from  the  anterior  and  antero- 
lateral produced  portion  of  the  valve,  by  the  development  of  a  partition 
which  is  apparently  a  continuation  of  the  gently  concave  or  flattened 
visceral  portion  of  the  valve ;  not  infrequently  the  specimens  break  along 
this  partition  separating  the  produced  portion  of  the  shell  entirely  from 
the  visceral  portion  and  giving  it  quite  a  different  aspect  from  the  entire 
shell.     Other  internal  characters  of  the  shell  not  observed. 

Remarks. — This  species  is  easily  recognized  on  account  of  the  sub- 
quadrangular  form  of  the  posterior  view  of  the  shell  due  to  the  broadly 
flattened  mesial  portion  of  the  pedicle  valve  and  the  nearly  vertical  posi- 
tion of  the  lateral  slopes  towards  the  cardinal  margin.  Other  characteris- 
tic features  of  the  species  are  the  short  hinge-line,  the  crowded  group 


1  18  MISSISSIPPI  \X    BRACHIOPODA 

of  spine  bases  on  and  adjaeenl  to  the  auriculations,  and  the  very  peculiar 
development  of  the  partition  from  the  inner  surface  of  the  brachial  valve 
which  so  completely  separates  the  visceral  from  the  anteriorly  produced 
portion  of  the  valve.  The  species  is  usually  rather  small,  but  examples 
with  a  length  of  30  mm.  or  more  are  not  infrequent  in  some  localities. 
In  mosl  localities  the  fasciculate  arrangement  of  the  COStSB  is  not  a  con- 
spicuous  feature  of  the  species. 
Horizon. — Chester  group. 

Genus  ECHIN0C0NCEU8  n.  gen. 

Description.  Shell  productoid  in  form  and  with  internal  characters  as 
in  the  genus  Productus.  The  external  surface  of  the  valves  marked  by 
more  or  less  sharply  differentiated  concentric  bands  which  commonly 
grow  broader  in  passing  from  the  beak  to  the  outer  margins,  each  band 
bearing  numerous,  crowded,  fine,  appressed,  imbricating  spines,  either 
subequal  or  unequal  in  size,  which  are  produced  from  elongate,  node- 
like bases. 

h'<  murks. — This  genus  is  proposed  to  include  those  shells  which  have 
heretofore  been  placed  in  the  genus  Productus  in  the  group  typified  by 
P.  pit  in-  In  I  us.  This  whole  group  of  species  differs  so  fundamentally 
from  the  members  of  the  genus  Productus  as  typified  by  the  genotype, 
/'.  si  mm  I icuhil us,  in  their  surface  markings,  that  it  has  long  seemed  to 
the  writer  that  they  should  be  separated  under  a  different  generic  name, 
although  their  internal  characters  are  essentially  alike.  The  genus  is 
represented  in  the  Mississippian  faunas  under  consideration  by  several 
species,  none  of  which  suggest  any  intergradation  with  those  of  the 
restricted  Productus. 

Eciiinoconchus  alternatus  (Norwood  and  Pratten) 
Plate  XVII,  Figs.  1-7 

1855.     Productus  alternatus  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci. 

Phil.,  (2),  vol.  3,  p.  20,  pi.  2,  figs.  la-e. 
1858.     Productus  vittatus  Hall,  Geol.  Iowa,  vol.  1,  pt,  2,  p.  639. 
1863.     Productus  gradatus  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2, 

p.  93. 
1883.     Productus  alternatus  Hall,  Rep.  N.  Y.   State   Geol.   for  1882,  pi. 

(18)  49,  fig.  14. 
1883.     Productus  vittatus  Hall,  Rep.  N.  T.  State  Geol.  for  1882   pi.  (18) 

49,  figs.  15-17. 
1892.     Productus  alternatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8    pt.  1, 

pi.  18,  fig.  14. 
1892.     Productus  vittatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  18, 

figs.  15r17. 
1894.     Productus  vittatus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  43. 

Description.  —  Shell  large,  usually  as  wide  or  wider  than  long,  but 
occasionally    longer     than    wide,    the    hinge-line    a    little    shorter     than 


ECHINOCONCHUS  139 

the  greatest  -width,  the  cardinal  extremities  obtusely  angular  or  a  little 
rounded.  The  dimensions  of  a  nearly  complete  example  are :  length 
from  hinge-line  to  front  margin  42  mm.,  length  from  umbonal  region  to 
front  margin  50  mm.,  greatest  width  49  mm.,  length  of  hinge-line  ±40 
mm.,  convexity  of  pedicle  valve  25  mm.,  depth  of  visceral  cavity  between 
the  two  valves  18  mm. 

Pedicle  valve  strongly  convex  with  the  point  of  greatest  convexity 
posterior  to  the  middle,  the  surface  curving  abruptly  to  the  cardinal 
margin,  less  abruptly  to  the  lateral  margins  and  more  gently  to  the 
anterior  margin,  compressed  towards  the  cardinal  extremities  in  sub- 
auriculate  expansions  which  are  not  sharply  differentiated  from  the 
general  surface,  the  umbonal  region  prominent  and  strongly  protuberant 
beyond  the  cardinal  margin ;  mesial  sinus  originating  in  the  umbonal 
region,  usually  of  moderate  depth,  rather  broad,  rounded  in  the  bottom 
and  ill  denned  laterally;  the  beak  strongly  incurved.  Surface  of  the 
valve,  in  the  exfoliated  condition,  marked  by  strong,  regular,  concentric 
bands  which  are  rather  abruptly  elevated  at  their  anterior  margin  with 
the  surface  sloping  regularly  to  the  line  of  elevation  of  the  next 
posterior  band,  these  bands  vary  in  width  from  1  to  5  mm.,  usually  being 
narrower  towards  the  beak  and  again  towards  the  front  margin  in 
mature  shells,  with  the  broadest  bands  in  the  middle  portion  of  the  valve ; 
when  the  surface  is  not  exfoliated  these  concentric  bands  bear  closely 
crowded,  fine,  appressed  spines  directed  anteriorly,  the  more  posterior 
rows  overlapping  those  in  front,  upon  each  concentric  band  the  coarser 
spines  are  along  its  anterior  margin,  the  more  posterior  ones  being  finer, 
with  a  narrow,  naked  area  along  the  posterior  border  of  each  band  nearly 
or  wholly  free  from  spines. 

Brachial  valve  concave  at  the  beak,  the  concavity  extending  anteriorly 
with  broadly  diverging,  but  indefinite  lateral  borders  which  intersect  the 
lateral  borders  of  the  valve  at  about  mid-length,  towards  the  cardinal 
extremities  the  surface  is  somewhat  flattened,  the  visceral  portion  not 
sharply  differentiated  from  the  produced  part ;  near  or  posterior  to  the 
middle  of  the  valve,  a  low,  but  rather  broad,  rounded,  ill-defined  mesial 
fold  originates  which  grows  more  prominent  anteriorly.  Surface  marked 
by  concentric  bands  and  fine,  appressed  spines  similar  to  those  of  the 
opposite  valve. 

Remarks.  —  It  is  not  clear  that  this  species  should  be  differentiated  from 
E.  punctatus  Martin,  but  this  form  having  its  most  typical  development  in 
the  Keokuk  limestone  commonly  has  been  considered  as  distinct  from 
the  Pennsylvanian  shell  usually  designated  by  Martin's  name.  The 
Keokuk  shell  has  a  proportionally  longer  hinge-line,  a  broader  umbonal 
region  and  more  obtusely  pointed  beak  than  the  Pennsylvanian  shell, 
and  the  concentric  bands  of  the  surface  are  usually  broader  and  stronger, 


140  MISSISSIPI'IAN    BHACHIOPODA 

with  the  spine  bases  smaller  and  less  numerous,  although  this  latter 
character  may  be  more  or  less  dependent  upon  the  state  of  preservation. 
Martin's  type  specimens  of  piinchihts  were  evidently  collected  in  the 
''Mountain  Limestone",  a  formation  equivalent  to  our  Mississippian, 
and  among  lus  original  illustrations  the  larger  specimens  seem  to  agree 
well  with  the  shells  from  the  Keokuk  limestone,  so  that  it  is  possible 
thai  his  name  should  be  applied  to  the  shells  here  under  consideration  and 
a  different  name  assigned  to  the  Pennsylvania!)  shells.  As  to  the  identity 
of  Norwood  and  Pralten's  /'.  tillcnuHvs  with  Hall's  P.  vitlatus,  there  can 
be  no  doubt;  the  identity  of  Swallow's  P.  gradatus  is  less  certain,  al- 
though it  is  probably  a  synonym  also.  Some  specimens  from  the  St.  Louis 
Limestone  have  a  shorter  hinge-line  and  narrower  umbo,  approaching 
more  nearly  the  lYimsy I vanian  shells,  and  should  perhaps  be  excluded 
from  t his  species. 

Horizon.  Burlington  limestone,  Keokuk  limestone,  ?St.  Louis  limestone, 
and   ?Okaw  formation  of  the  Chester  group. 

ECHINOCONCHUS   (iKNKVIKVENSIS  n.   sp. 

Plate  XVIII,  Figs.  1-6 

Description.  —  Shell  a  little  above  medium  size,  broader  than  long,  the 
hinge-line  much  shorter  than  the  greatest  width,  the  greatest  width 
anterior  to  the  mid-length.  The  dimensions  of  a  nearly  complete  pedicle 
valve  are:  length  from  hinge-line  to  front  margin  22.2  mm.,  length  from 
umbonal  region  to  front  margin  27.6  mm.,  greatest  width  31  mm.,  length 
of  hinge-line  21  mm.,  convexity  31  mm. 

Pedicle  valve  strongly  convex  with  the  greatest  depth  posterior  to  the 
middle,  the  umbonal  region  prominent  but  rather  narrow,  protuberant 
posteriorly  beyond  the  hinge-line,  the  surface  curving  abruptly  to  the 
cardinal  margin,  curving  more  gently  to  the  lateral  and  anterior  margins, 
only  slightly  compressed  towards  the  cardinal  extremities ;  mesial  sinus 
originating  posteriorly  in  the  umbonal  region,  it  is  of  only  moderate  width 
and  depth,  rounded  in  the  bottom  and  ill  denned  laterally ;  the  beak 
rather  small,  pointed  and  strongly  incurved.  Surface  marked  by  regular, 
more  or  less  well-defined,  concentric  bands  from  two  to  four  millimeters 
in  width,  upon  which  are  the  elongate  bases  of  fine,  crowded,  appressed 
spines,  those  near  the  front  of  each  band  being  finer  than  those  situated 
posteriorly. 

Brachial  valve  gently  concave  throughout,  except  towards  the  cardinal 
extremities,  which  are  flattened,  near  or  posterior  to  the  middle  of  the 
valve,  a  low,  rounded,  mesial  fold  originates  which  becomes  a  little 
stronger  towards  the  front.  The  surface  marked  by  concentric  bands 
and  appressed  spines  similar  to  those  of  the  opposite  valve. 


KCIIINOCONCHUS  141 

Remarks.— This  species  is  much  like  E.  altematus  of  the  Keokuk  lime- 
stone, but  mature  examples  are  always  much  smaller  than  in  that 
species,  the  hinge-line  is  proportionally  shorter,  the  umbonal  region  is 
much  narrower  and  more  sharply  pointed  towards  the  beak.  These 
characters  arc  apparently  constant  and  the  shell  is  so  commonly  found 
in  the  Ste.  Genevieve  limestone  that  it  has  seemed  best  to  recognize 
it  as  a  good  species,  although  a  broad  interpretation  of  E.  punctatus  might 
include  not  only  this  form  but  E.  alternatus  as  well. 

Horizon. — Ste.  Genevieve  limestone. 

ECHINOCONCHUS  BISERIATUS    (Hall) 

Plate  XVII,  Figs.  10-15 

1855.  Product  us  fimbria  I  us  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci. 

Phil.  (2),  vol.  3,  p.  19  (not  P.  fimbriatus  Sowerby). 

1856.  Product  us  biseriatus  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  12. 

1882.  Productus  biseriatus  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

pi.  6,  figs.  8-12. 

1883.  Productus  biseriatus  Hall,  12th  Rep.  Geol.  Surv.  Ind.,  p.  325,  pi. 

29.  figs.  8-12. 
1894.     Productus  biseriatus  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  43. 
1906.     Productus  biseriatus  Beede,  30th  Ann.  Rep.   Geol.   Surv.  Ind.,  p. 

1291).  pi.  19,  fig.  6 ;  pi.  22,  figs.  8-12. 
1911.     Productus  biseriatus  Girty,  Bull.  U.  S.  Geol.  Survey  No.  439,  p.  46, 

pi.  3,  figs.  10-11. 

Description.— Shell  small,  length  and  width  usually  about  equal,  but 
varying  from  longer  than  wide  to  wider  than  long,  the  hinge-line 
shorter  than  the  greatest  width,  the  greatest  width  near  or  anterior  to 
the  mid-length,  the  cardinal  extremities  obtusely  angular  or  a  little 
rounded.  The  dimensions  of  a  nearly  perfect  specimen  are :  length 
from  hinge-line  to  front  margin  11.4  mm.,  length  from  umbonal  region 
of  pedicle  valve  to  front  margin  13.7  mm.,  greatest  width  13.5  mm., 
length  of  hinge-line  10  mm.,  convexity  of  pedicle  valve  7  mm.,  depth 
of  visceral  cavity  between  the  two  valves  4.4  mm. 

Pedicle  valve  strongly  convex,  the  umbonal  region  pointed  and  pro- 
tuberant beyond  the  hinge-line,  the  surface  curving  abruptly  to  the 
cardinal  margin,  more  gently  to  the  lateral  and  anterior  margins,  com- 
pressed at  the  cardinal  extremities  to  form  small  auriculations  which 
are  not  sharply  differentiated  from  the  lateral  slopes ;  mesial  sinus  obso- 
lete ;  beak  pointed  and  strongly  incurved  beyond  the  hinge-line.  Surface 
marked  by  regular  concentric  bands  which  are  differentiated  by  a  slight 
elevation  of  the  surface  along  their  anterior  margin,  upon  each  concentric 
band  is  a  row  of  elongate  nodes,  highest  in  front,  the  bases  of  appressed 
spines,  which  become  lower  posteriorly  and  disappear  in  front  of  the 
posterior  margin  of  the  band ;  closely  crowded  between  and  in  front  of 
these  larger  nodes  are  numerous  finer  but  entirely  similar  nodes  which 


142  MISS1SSIPPIAN   BRACIIIOI'ODA 

arc  the  bases  of  finer  appressed  spines;  the  spines  themselves  are  com- 
monly destroyed,  lull  they  are  doubtless  entirely  similar  to  those  of 
P.  punctatus. 

Brachial  valve  concave,  the  central  concavity  narrower  at  the  beak 
and  rapidly  broadening  towards  the  front,  with  the  surface  somewhat 
flattened  and  subauriculate  towards  the  cardinal  extremities;  mesial  fold 
absent.  Surface  marked  by  concentric  bands  similar  to  those  of  the  op- 
posite Aralve  and  with  similar  appressed  spine  bases. 

E<  marks.— This  little  species  is  clearly  of  the  type  of  E.  alternatus, 
from  which  species  it  differs  chiefly  in  its  much  smaller  size  and  in  the 
absence  of  a  mesial  sinus  in  the  pedicle  valve  and  fold  in  the  brachial 
valve.     One  of  the  largest  examples  observed  has  a  length  of  18  mm. 

Horizon. — Salem  limestone. 

ECIIINOCONCHUS  MORBILLIANUS    (Wilichell) 

Plate  XVIII,  Figs.  13-15 

1865.     Produchis  morbilliamts  Wiinchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p. 
113. 

Description. — Shell  small,  a  little  wider  than  long,  the  hinge-line  shorter 
than  the  greatest  width,  the  greatest  width  anterior  to  the  mid-length, 
the  cardinal  extremities  obtusely  subangular.  The  dimensions  of  a  nearly 
complete  pedicle  valve,  the  holotype,  are :  length  from  hinge-line  to  front 
margin  12  mm.,  length  from  umbonal  region  to  front  margin  13.8  mm., 
greatest  width  14.5  mm.,  length  of  hinge-line  12  mm.,  convexity  6  mm. 

Pedicle  valve  strongly  convex,  the  greatest  depth  posterior  to  the 
middle,  the  umbonal  region  prominent  and  somewhat  protuberant  poste- 
riorly beyond  the  hinge-line,  the  surface  curving  abruptly  to  the  cardinal 
margin  on  each  side  of  the  beak,  and  much  more  gently  to  the  lateral  and 
anterior  margins,  compressed  at  the  cardinal  extremities  to  form  small 
auricular  expansions ;  mesial  sinus  obsolete ;  the  beak  small,  pointed  and 
strongly  incurved.  Surface  marked  by  regular,  concentric  bands  whose 
width  at  the  median  line  of  the  valve  is  1  to  1.5  mm.,  each  band  is  slightly 
depressed  posteriorly  below  the  anterior  margin  of  the  band  next  behind, 
and  each  is  marked  by  the  radially  arranged  and  nearly  uniform  elongate 
bases  of  fine,  appressed  spines,  higher  in  front  where  the  spines  have  be- 
come free  and  becoming  obsolete  posteriorly  at  or  near  the  posterior 
margin  of  the  concentric  band ;  towards  the  cardinal  extremities  the  reg- 
ular arrangement  of  the  concentric  bands  and  spine  bases  becomes  some- 
what disorganized. 

Brachial  valve  not  known. 

Rem  arks.— This  little  Echinoconchus  most  closely  resembles  the  small 
E.  biscriatus  of  the  Salem  limestone.  These  two  species  are  similar  in 
size  and  in  both  the  mesial  sinus  is  wanting.       E.  morbillianus  is  perhaps 


STROPHALOSIA  143 

more  narrowly  rounded  transversely  across  the  median  part  of  the  pedicle 
valve,  in  consequence  of  which  the  lateral  slopes  curve  less  abruptly  to 
the  lateral  margins,  but  ;i  larger  number  of  examples  should  be  examined 
to  determine  this  ;is  a  constant  character.  The  most  essential  difference 
between  the  two  species  is  in  the  character  of  the  fine  appressed  spines 
which  are  essentially  uniform  in  size  upon  E.  morbillianus  with  more 
elongate  bases,  while  in  E.  biseriatus  the  spine  bases  occur  in  two  distinct 
sizes,  larger  ones  posteriorly  upon  each  band  Avith  much  smaller  and  more 
numerous  ones  closely  crowded  anteriorly. 

A  second  example  of  the  species  is  mentioned  by  Wine-hell,  "a  cast  from 
the  Yellow  Sandstone  below  (probably  No.  5),"  as  being  probably  iden- 
tical. A  careful  examination  of  the  two  specimens,  however,  clearly  in- 
dicates that  they  are  not  the  same  species,  and  furthermore  the  Yellow 
Sandstone  specimen  is  probably  a  Productclla. 

Horizon. — Base  of  Burlington  limestone. 

Genus  STEOPHALOSIA  King 

Description.  —  Shells  resembling  Productus  or  Productclla  in  general 
form,  with  a  distinct  cicatrix  on  the  umbo  of  the  pedicle  valve  at  the 
point  where  they  have  been  attached  by  the  shell  substance  to  some  ex- 
ternal object,  or  attached  by  nearly  the  entire  outer  surface  of  the  pedicle 
valve.  Pedicle  valve  with  a  well-defined  cardinal  area,  the  delthyrium 
closed  by  a  deltidium,  cardinal  teeth  prominent  but  not  supported  by 
dental  lamellae.  Brachial  valve  with  a  narrower  cardinal  area,  the  car- 
dinal process  erect,  bifid  on  its  anterior  and  trifid  on  its  posterior  face, 
supported  laterally  by  the  socket  plates  and  continued  anteriorly  into  a 
median  septum  which  extends  half  the  length  of  the  valve.  Surface  of  the 
pedicle  valve  spinose,  the  spines  near  the  beak  often  recurved  and  em- 
bracing some  external  object,  and  in  some  species  all  the  spines  assisting 
in  the  attachment  of  the  shell.  Brachial  valve  either  spinose,  lamellose,  or 
smooth  externally. 

Remarks. — Among  the  species  which  have  been  referred  to  the  genus 
Strophalosia  in  the  present  report  are  two  rather  distinct  types.  One  of 
these  contains  small  species,  such  as  8.  scintilla  and  8.  keokuk,  which  are 
attached  to  other  brachiopod  or  mollusc  shells  by  essentially  the  entire 
outer  surface  of  the  pedicle  valve,  the  surface  spines  being  little  root-like 
processes  which  grow  outward  from  the  shell  margin  in  all  directions  in 
close  attachment  throughout  their  entire  length.  The  other  type  of  shell 
is  larger  and  was  attached  during  life  by  the  umbonal  portion  of  the 
pedicle  valve  only,  being  represented  by  the  two  species  S.  cymbula  and 
S.  beecheri. 


144  MISSISSII'PIAN   BRACIJIOPODA 

Steophalosia  scintilla  Beeeher 
Plate  XVIII,  Figs.  19-23 

1890.    Strn/.luilosKi  scintilla  Beeeher,  Am.  -lour.  Sei.  (3),  vol.  40,  p.  243, 

pi.  9,  figs.  10-13. 
L892.     Strophcdosia  scintilla   Hall   and  Clarke.   Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  15B,  figs.  32-34. 
1908.     Sh'ojihalosin  siiiiiilla  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

L'tid  ser.,  ]).  7(i,  pi.  17,  figs.  26-29. 

Description.  Shell  very  small,  attached  to  foreign  objects  by  nearly  the 
ciil  ire  surface  of  Hie  pedicle  valve,  wider  than  long,transversely  subellip- 
tical  in  outline  with  the  posterior  margin  truncated,  the  hinge-line  a  little 
shorter  than  the  greatest  width.  The  dimensions  of  a  nearly  complete 
example  are:  Length  L.9  mm.,  width  3.1  mm. 

Pedicle  valve  adherent  to  foreign  objects,  usually  to  shells  of  other 
brachiopods,  its  margin  elevated  and  usually  furnished  with  a  variable 
number  of  slender,  procumbent  spines,  rarely  more  than  six  or  seven  in 
number  and  sometimes  wholly  wanting,  the  spines  rarely  or  never  occur 
along  the  cardinal  margin;  cardinal  area  low  and  broadly  triangular,  with 
a  small  delthyrium  closed  by  a  deltidium,  the  hinge-teeth  small,  but  well 
developed,  unsupported  by  dental  lamellae.'. 

Brachial  valve  convex  at  the  beak,  becoming  flat  or  concave  anteriorly ; 
the  beak  inconspicuous,  scarcely  or  not  at  all  extended  beyond  the  hinge- 
line  ;  the  surface  marked  by  concentric  lines  of  growth. 

Internally  the  adductor  muscular  scars  are  small  and  the  surface  is 
pustulose  near  the  margin ;  the  brachial  impressions  have  not  been 
observed. 

Remarks. — This  species  is  the  smallest  member  of  the  genus  so  far 
known  in  the  faunas  under  consideration.  It  resembles  S.  keokuk  in  the 
almost  complete  attachment  of  the  pedicle  valve  to  foreign  objects,  but  it 
differs  from  that  species,  in  addition  to  its  smaller  size,  in  the  smaller 
number  and  less  crowded  attaching  spines,  and  in  the  apparent  absence 
of  these  spines  along  the  cardinal  margin.  This  last  character  seems  to 
be  a  good  one  for  the  species,  in  no  case  have  the  spines  been  observed 
growing  from  the  central  portion  of  the  cardinal  margin,  and  in  only  one 
or  two  examples  have  they  seemed  to  be  present  at  one  of  the  outer  ex- 
tremities of  this  margin,  even  these  not  being  so  well  preserved  as  to  make 
it  certain  that  they  are  spines. 

Horizon. — Louisiana  limestone  of  the  Kinderhook. 


STEOPHALOSIA  145 

Strophalosia  keokuk  Beecher 
Plate  XVIII,  Figs.  17-18 

1890.     Strophalosia  KeokvJc  Beecher,  Am.  Jour.  Sci.   (3).  vol.  40,  p.  244, 

pi.  9,  figs.  18-24. 
1892.     Strophalosia  Keokuk  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi. 

17A,  figs.  5-7. 

Description.— Shell  small,  attached  to  external  objects  by  nearly  the 
entire  pedicle  valve,  broader  than  long,  subelliptical  in  outline,  truncated 
on  the  cardinal  margin,  the  hinge-line  a  little  shorter  than  the  greatest 
width.  The  dimensions  of  a  nearly  complete  example  are :  length  3.8 
mm.,  width  4.3  mm. 

Pedicle  valve  adherent  to  foreign  objects,  all  the  specimens  observed 
being  attached  to  shells  of  Phityceras,  its  margin  elevated  and  furnished 
with  numerous,  slender,  often  croAvded  and  rather  elongate,  procumbent 
and  attached  spines  which  occur  as  commonly  along  the  cardinal  margin 
as  elsewhere ;  cardinal  area  low  and  broadly  triangular,  with  a  narrowly 
triangular  delthyrium  closed  by  a  deltidium;  the  hinge-teeth  well  devel- 
oped, not  supported  by  dental  lamellae. 

Brachial  valve  with  a  small  umbonal  convexity  in  front  of  the  beak, 
beyond  which  it  becomes  flat  or  concave ;  the  surface  marked  by  concen- 
tric lines  of  growth. 

Remarks.  —  This  species  is  of  the  type  of  S.  scintilla,  but  grows  some- 
what larger,  and  is  often  proportionally  more  elongate.  It  differs  es- 
pecially from  that  species  in  the  more  numerous,  more  elongate,  and  more 
crowded  spines  of  attachment  which  occur  as  commonly  along  the  car- 
dinal margin  as  elsewhere. 

Horizon. — Keokuk  (Crawfordsville  shale,  Indiana). 

Strophalosia  cymbula  Hall  and  Clarke 
Plate  XIX,  Figs.  35-36 

1892.     Strophalosia  cymbula  Hall  and  Clarke,  Pal.  N.  T.,  vol.  8,  pt.  1, 

pi.  17A,  figs.  3-4,  8-9. 
1897.     Strophalosia  cymbula  Hall,  14th  Rep.  N.  Y.  State  Geol.,  p.  355, 

pi.  7,  fig.  5. 

Description. — Shell  of  about  medium  size  or  smaller,  not  attached  in  the 
mature  condition,  broader  than  long,  the  hinge-line  nearly  equaling  the 
greatest  width,  the  cardinal  extremities  angular.  The  dimensions  of  one 
of  the  co-types  are :  length  19.8  mm.,  width  22.5  mm.,  convexity  of  pedicle 
valve  7  mm.,  height  Of  cardinal  area  1.6  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  near  the 
middle,  the  beak  a  little  distorted,  the  cicatrix  small  and  inconspicuous, 
the  surface  rather  regularly    convex    except    towards  the    cardinal    ex- 


146  \i  ississni'i  \x    BRACHIOPODA 

tremities,  where  it  is  compressed;  cardinal  area  broadly  triangular, 
the  cardinal  margins  sharply  angular  and  nearly  straight  or  gently 
convex  from  the  beak  to  the  cardinal  extremities,  its  surface  nearly 
flal  and  lying  nearly  in  the  plane  of  the  valve;  the  delthyrium  small, 
partially  closed  by  the  deltidium,  which  may  be  incomplete  in  the  speci- 

n  observed.     The  surface  covered  with  appressed  spines  of  moderate 

size  whose  liases  occur  at  intervals  of  about  2  mm.  and  tend  to  be 
arranged  in  radiating  series,  inconspicuous  or  absent  from  the  umbonal 
region;  surface  marked  also  by  inconspicuous  concentric  lines  of  growth. 

Brachial  valve  concave,  its  curvature  following  somewhat  closely  that 
of  the  opposite  valve,  deflected  towards  the  cardinal  extremities;  the  beak 
inconspicuous;  the  cardinal  area  much  narrower  than  that  of  the  op- 
posite valve;  the  surface  marked  by  more  or  less  irregular,  concentric 
lines  of  growth  with  no  spine  bases. 

Remarks. — This  species,  figured  but  not  described  by  Hall  and  Clarke, 
is  the  largesl  which  has  been  recognized  in  our  Mississippian  faunas. 
It  resembles  8.  beecheri,  but  is  larger,  with  more  conspicuous  spine  bases 
upon  the  pedicle  valve. 

Horizon. — Kinderhook  (New  Providence  shale,  Kentucky). 

Stropiialosia  beecheri  Rowley 
Plate  XIX,  Figs.  37-38 

1893.     Strophalosia   beecheri   Rowley,  Am.  Geol.,  vol.  12,  p.  308,  pi.  14, 

figs.  18-19. 
1908.     Strophalosia  beecheri  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  76,  pi.  17,  figs.  24-25. 

Description.  —  Shell  unsymmetrical,  below  medium  size,  not  attached  in 
the  mature  condition,  broader  than  long,  the  hinge-line  less  than  the 
greatest  width,  the  cardinal  extremities  obtusely  angular.  The  dimen- 
sions of  the  holotype,  a  pedicle  valve,  are:  length  13.2  mm.,  greatest 
width  14.8  mm.,  length  of  hinge-line  11  mm.,  convexity  6  mm. 

Pedicle  valve  most  convex  near  the  middle,  the  surface  sloping  with  a 
gently  convex  curvature  to  the  beak,  to  the  antero-lateral  and  anterior 
margins,  compressed  towards  the  cardinal  extremities,  the  umbonal  region 
projecting  slightly  beyond  the  cardinal  margin,  the  cicatrix  small  and 
inconspicuous ;  cardinal  area  rather  narrow  and  nearly  flat,  lying  in 
nearly  the  plane  of  the  valve,  the  delthyrium  small,  closed  by  a  convex 
deltidium.  Surface  marked  by  irregular,  concentric  lines  of  growth,  and 
by  rather  strong  spine  bases  which  seem  to  be  arranged  in  rather  irregu- 
lar concentric  lines,  the  distances  between  the  spines  being  about  2  mm. 
or  somewhat  less,  the  spines  themselves  have  been  destroyed  but  judging 
from  the  position  of  the  bases  they  must  have  been  nearly  erect. 

Brachial  valve  not  known. 


RHIPIDOMEU.A  147 

"Remarks. — This  species  has  been  established  upon  a  single  unique  speci- 
men, a  pedicle  valve,  which  is  not  unlike,  in  its  general  appearance,  a 
somewhat  distorted  pedicle  valve  of  Product ella  pyxidata,  with  which  it 
is  associated.  The  presence  of  a  well-defined  cardinal  area,  however, 
excludes  the  specimen  at  once  from  the  genus  Productella.  The  species 
is  somewhat  similar  to  S.  cymbida,  but  is  smaller,  with  a  relatively  more 
convex  pedicle  valve,  and  with  the  surface  spines  more  erect  in  position 
and  not  arranged  in  radiating  series. 

Horizon. — Louisiana  limestone. 

Family  ORTHID^ 

Genus  RHIPIDOMELLA  Oehlert 

Description.— Shell  subcircular  or  subovate  in  outline,  biconvex  and 
sublenticular,  with  the  brachial  valve  somewhat  the  deeper.  Hinge-line 
short,  cardinal  areas  narrow,  especially  that  of  the  brachial  valve.  The 
pedicle  valve  with  two  strong,  diverging  hinge-teeth,  from  the  base  of 
each  a  more  or  less  strongly  defined  curved  ridge  extends  anteriorly, 
bordering  the  muscular  scar.  The  muscular  area  large,  flabelliform,  and 
deeply  impressed,  the  margin  thickened  and  elevated ;  the  pedicle  scar 
occupies  the  entire  rostral  cavity,  the  adductor  scars  rather  small,  narrow 
and  elongate,  entirely  surrounded  by  the  large  diductor  scars,  from 
the  narrow  adductor  scar  a  median  ridge  extends  anteriorly,  dividing  the 
diductors.  The  brachial  valve  with  deep  and  narrow  dental  sockets,  the 
socket  plates  prominent,  sometimes  supporting  short  crura;  the  cardinal 
process  erect,  produced  anteriorly  in  the  floor  of  the  valve  as  a  median 
ridge ;  the  muscular  area  small,  quadripartite,  usually  indistinct.  The 
surface  of  both  valves  marked  by  fine,  rounded,  subequal,  hollow  cost*, 
often  opening  on  the  surface,  the  openings  probably  representing  the 
broken  bases  of  fine,  hollow  spines. 

Remarks. — In  external  features  the  members  of  this  genus  are  much 
alike  in  outline  and  general  contour  of  the  shell,  and  practically  all  of 
them,  except  R.  dmbia,  might  from  their  external  characters  alone,  be 
included  in  the  European  species  R.  michelinia  as  it  has  been  interpreted 
by  European  authors.  This  interpretation  of  the  American  form  has 
sometimes  been  suggested,1  but  a  most  careful  study  of  many 
examples  has  brought  out  the  fact  that  essentially  all  of  the  species 
which  have  been  described  from  our  American  Mississippian  faunas  are 
good  species,  although  their  most  essential  characters  have  not  always 
been  pointed  out,  and  that  several  additional  species  must  be  recognized. 

The  most  important  characters  for  use  in  the  differentiation  of  species 
are  the  form  of  the    cardinal   process  and  socket  plates  of  the    brachial 

iWeller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  296   (1909). 


1  IS  MISSISSMTl.W     BBACHIOPODA 

valve,  and  the  size  and  strength  of  the  muscular  impressions  of  both 
valves.  Externally  the  species  differ  somewhat  in  general  proportions, 
contour  and  surface  markings,  and  although  these  differences  are  fre- 
quently slight,  thej  correlate  with  the  more  marked  internal  features. 

KlIII'IDUMKU.A     MISSOI   KIKNSIS    (Swallow) 

Plate  XX,  Figs.  1-8 

L860.     Ortkis  Missouriensis  Swallow,  Trans.   St.  Louis  Acad.   Sci.,  vol.  1, 

p.  639. 
1892.    Orthis  Missouriensis  Hall  and  Clarke.  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi. 

6A,  figs.  L6-17. 
1908.     Rhipidomella  missouriensis  Rowley.   Mo.   Bureau  Geol.  and  Mines, 

vol.  8,  2nd  ser,  p.  78,  pi.  17.  figs.  4:5-47. 

Description.  Shell  lenticular  in  form,  of  medium  size  or  a  little  smaller. 
suborbicular  in  outline,  usually  a  little  wider  than  long,  the  greatest 
width  a  little  anterior  to  the  middle,  the  hinge-line  much  shorter  than 
the  greatesl  width  of  the  shell,  the  cardinal  extremities  rounded.  The 
dimensions  of  I  wo  examples  of  about  average  size  are:  length  of  pedicle 
valve  19.7  mm.  and  18.1  mm.,  length  of  brachial  valve  19.1  mm.  and  18 
mm.,  greatest  width  23.5  mm.  and  20.5  mm.,  length  of  hinge-line  8.5  mm. 
and  9.5  mm.,  thickness  8  mm.  and  9  mm. 

Pedicle  valve  most  convex  in  the  umbonal  region,  the  surface  curving 
somewhat  abruptly  to  the  cardinal  margin  and  compressed  towards  the 
cardinal  extremities,  broadly  flattened  in  the  median  portion  of  the  valve 
and  becoming  gently  convex  towards  the  antero-lateral  and  anterior 
margins ;  mesial  sinus  obsolete  or  present  only  as  a  slight  depression 
close  to  the  anterior  margin;  beak  small,  pointed,  a  little  incurved;  car- 
dinal area  small,  concave,  becoming  more  curved  towards  the  beak,  the 
inferior,  flatter  portion  lying  at  an  angle  of  about  45  degrees  to  the  plane 
of  the  valve ;  delthyrium  wider  than  high,  its  Avidth  at  the  base  being 
from  one-fourth  to  one-third  the  total  Avidth  of  the  cardinal  area.  In- 
ternally the  hinge-teeth  are  large,  strong,  and  slightly  diverging;  the 
flabellate  or  suboA^ate  muscular  scars  reach  anteriorly  to  the  middle,  or  to 
a  point  beyond  the  middle  of  the  valve,  and  are  limited  externally  by  a 
slightly  raised  border,  the  adductor  impressions  do  not  extend  to  the  an- 
terior margin  of  the  entire  scar,  but  a  raised  median  ridge  continues  an- 
teriorly to  the  limits  of  the  diductor  scars;  the  unpaired  pedicle  muscular 
scar  occupies  the  rostral  portion  of  the  valve ;  its  surface  is  slightly  raised 
above  that  of  the  contiguous  scars  in  front  and  is  sharply  differentiated 
from  them;  the  anterior  and  lateral  margins  of  the  valve  are  slightly 
thickened  and  crenulate  internally. 

Brachial  valve  a  little  more  convex  than  the  pedicle,  its  greatest  con- 
vexity near  or  a  little  posterior  to  the  middle,  the  surface  curving  more 


RHIPIDOMELLA  149 

abruptly  to  the  cardinal  margin,  slightly  compressed  towards  the  car- 
dinal extremities,  towards  the  anterior  margin  the  surface  is  gently 
convex  and  towards  the  lateral  margins  a  little  more  strongly  so ;  the 
median  portion  of  the  valve  is  slightly  flattened  and  is  not  infrequently 
a  little  impressed  along  the  median  line  to  form  a  very  shallow,  ill- 
defined  sinus,  which,  with  the  slight  flattening  of  the  opposite  valve, 
sometimes  makes  the  outline  of  the  shell  a  little  emarginate  in  front;  the 
beak  is  small,  obtusely  pointed  and  scarcely  incurved;  the  cardinal  area 
is  a  little  smaller  than  that  of  the  opposite  valve  and  lies  in  nearly  the 
plane  of  the  valve.  Internally  the  cardinal  process  is  rather  large  and 
is  continued  as  a  flattened  median  ridge  along  the  floor  of  the  valve 
dividing  the  quadripartite  muscular  impression ;  the  socket  plates  are 
prominent  and  widely  diverging,  with  deeply  excavated  dental  sockets ; 
the  muscular  scars  smaller  and  less  deeply  impressed  than  those  of  the 
opposite  valve. 

The  surface  of  both  valves  marked  by  nearly  uniform,  rounded  costal, 
about  three  or  sometimes  four  of  which  occupy  the  space  of  one  milli- 
meter, and  which  increase  by  bifurcation  and  intercalation ;  the  shell  sub- 
stance is  pierced  by  radiating  canals  or  tubes  which  follow  the  direction 
of  the  costa1  and  which  open  at  intervals  to  the  exterior  along  the  tops  of 
the  costa?.  Regular,  concentric  lines  of  growth  are  usually  present  which 
often  become  more  or  less  crowded  towards  the  front  margin. 

Remarks.  —  This  species  may  be  distinguished  from  E.  burling  ton  ensis, 
which  it  resembles,  by  its  proportionally  broader  form,  the  smaller  and 
less  extended  beak  of  the  pedicle  valve,  by  the  somewhat  more  strongly 
developed  radiating  costae  and  by  the  less  frequent  openings  of  the  radial 
canals  upon  the  shell  surface,  all  of  which  are  of  uniform  size.  The  size 
of  the  species  is  usually  less  than  that  of  R.  burlingtonensis. 

Horizon. — Louisiana  limestone. 

Rhipidomella  burlingtonensis    (Hall) 
Plate  XXI,  Figs.  5-7 ;  Plate  LXXXIII,  Figs.  7-8 

1858.     Orthis  michelini  var.  burlingtonensis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2, 

p.  596,  pi.  12,  figs.  4a-b.  " 
1874.     Orthis  Michelini  var.    Burlingtonensis?    White,  Prelim.  Rep.  Inv. 

Foss.,  p.  17. 
1892.     Orthis  Burlingtonensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1, 

pi.  6 A,  fig.  13. 
1892.     Orthis     (Rhipidomella)     Burlingtonensis    Hall    and   .Clarke,   Pal. 

N.  Y.,  vol.  8,  pt.  1,  pi.  20,  figs.  5-6. 
1894.     Orthis  burlingtonensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  63,  pi.  38, 

fig.  7. 
Description.— Shell  of  medium  size  or  larger,  subovate  in  outline,  the 
length  and  width  nearly  equal  or  wider  than  long,  the  greatest  width 


150  MlSSISSll'I'IAN    BRACHIOPODA 

near  or  a  little  anterior  to  the  middle,  the  hinge-line  Less  than  one-half 
the  greatesl  width  of  the  shell,  the  cardinal  extremities  rounded.  The 
dimensions  of  two  pedicle  valves  arc:  Length  26. <s  mm.  and  24  nun.,  width 
28.3  mm.  and  25  nun.,  Length  of  binge-line  10  mm.  and  11.8  mm.,  convexity 
(i.G  nun.  and  (i  nun.  The  dimensions  of  a  large  brachial  valve  are:  length 
28  mm.,  width  31J  mm.,  convexity  6.5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbo  rather 
prominent,  the  surface  sloping  abruptly  to  the  cardinal  margins,  some- 
times a  little  compressed  towards  the  cardinal  extremities,  curving  much 
more  gently  to  the  lateral  and  anterior  margins;  the  mesial  portion  of 
the  valve  broadly  and  indefinitely  flattened  anterior  to  the  middle,  some- 
times very  slightly  sinuate  near  the  front  margin;  beak  rather  prominent; 
cardinal  area  small,  concave,  with  the  curvature  increasing  towards  the 
beak,  the  lower,  flatter  portion  sloping  posteriorly  at  an  angle  of  about 
60  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply  defined, 
the  dclthyrium  large  and  broadly  triangular,  its  basal  width  sometimes 
occupying  fully  one-third  of  the  total  length  of  the  hinge-line.  Internally 
the  cardinal  teeth  are  of  moderate  strength  and  widely  divergent;  the 
muscular  scars  are  large  and  flabellate  with  a  slight  raised  marginal 
border,  reaching  beyond  the  middle  of  the  valve  anteriorly,  sometimes 
being  fully  two-thirds  the  total  length,  with  a  width  of  from  one-half 
to  two-thirds  the  total  width  of  the  valve,  the  adductor  scars  are  large 
and  well  defined,  resting  upon  a  somewhat  elevated  area  near  the  middle 
of  the  entire  muscular  region  which  is  continued  anteriorly  to  the  limits 
of  the  diductor  scars  in  a  raised  median  ridge  somewhat  narrower  than 
the  adductor  scars  themselves,  the  diductor  scars  are  very  large  and  are 
marked  by  several  slight,  subangular,  radiating  ridges,  the  unpaired 
pedicle  muscle  scar  is  large,  occupying  the  entire  rostral  portion  of  the 
valve  and  is  sharply  differentiated  from  the  contiguous  scars  in  front ; 
the  inner  margin  of  the  valve  is  erenulate  anteriorly  and  laterally. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  the  surface  sloping  with  a  gently  convex  curvature 
in  all  directions,  the  cardinal  extremities  sometimes  slightly  compressed; 
the  mesial  portion  of  the  valve  obscurely  flattened  or  sometimes  very 
slightly  impressed  in  an  ill-defined  sinus ;  beak  small,  not  incurved ;  car- 
dinal area  small,  lying  in  nearly  the  plane  of  the  valve.  Internally  the 
socket  plates  are  prominent,  with  their  anterior  extremities  almost  crura- 
like  in  form;  they  rest  upon  the  floor  of  the  valve  through  almost  their 
entire  length  and  are  widely  divergent ;  the  cardinal  process  is  prominent 
and  highly  elevated,  its  posterior  surface  is  nearly  vertical  and  sometimes 
trilobate  towards  the  apex,  the  anterior  surface  slopes  obliquely  to  the 
floor  of  the  valve  and  continues  as  a  low,  ill-defined  mesial  ridge  to  the 
anterior  margins  of  the  muscular  scars ;  muscular    scars  smaller  than 


KMIPIDOMELLA  151 

those  of  the  opposite  valve  and  less  deeply  impressed,  quadripartite  and 
subquadrate  in  outline;  the  inner  margin  of  the  valve  crenulate  anter- 
iorly and  laterally. 

Surface  of  both  valves  marked  by  regular,  uniform,  depressed,  rounded, 
radiating  costse,  from  two  to  three  of  which  occupy  one  millimeter.  The 
shell  substance  is  pierced  by  radiating  canals  or  tubules  of  two  sizes, 
which  apparently  follow  the  direction  of  the  costse,  the  larger  ones  open 
at  intervals  along  the  summits  of  the  costse  while  openings  of  the  finer 
ones  cover  the  sides  of  the  costs  and  the  furrows,  giving  to  the  shell, 
when  a  little  weathered,  the  appearance  of  being  punctate. 

Remarks. — This  species  is  characterized  by  the  prominent  umbo  of  the 
pedicle  valve,  by  the  greatly  elevated  cardinal  process  of  the  brachial 
valve  and  by  the  large  size  of  the  muscular  scars  in  the  pedicle  valve. 
In  size  it  is  about  equal  to  R.  oweni,  but  it  is  proportionally  longer  and 
has  a  much  more  prominent  umbo  on  the  pedicle  valve  and  nearly  or 
quite  obsolete  sinus  in  the  brachial  valve.  It  differs  from  R.  jerseyemis 
in  its  coarser  surface  costa\  the  different  position  of  the  cardinal  area 
of  the  pedicle  valve,  and  in  ils  much  more  prominent  cardinal  process. 
The  punctate  appearance  of  the  shell  surface  is  commonly  more  con- 
spicuous in  this  species  than  in  any  of  the  others  here  described,  but  this 
may  be  due  to  the  different  condition  of  preservation. 

Horizon.— Burlington  limestone. 

Rhipidomella  oweni  Hall  and  Clarke 
Plate  XXI,  Figs.  1-4 

1882.     Orthis  Michelini  (?)  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.  (6) 

36,  figs.  19-21. 
1892.     Orthis  (Rhipidomella)   Oweni  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8, 

pt.  1,  p.  342,  pi.  6,  figs.  19-21. 
1897.     Orthis   (Rhipidomella)   Oweni  Hall,  14th  Rep.  N.  Y.  State  Geol., 

p.  341,  pi.  4,  figs.  24-26. 

Description.  —  Shell  above  medium  size,  lenticular  in  form,  broader  than 
long,  with  the  greatest  width  anterior  to  the  middle,  the  hinge-line  about 
one-half  or  less  than  one-half  the  greatest  width  of  the  shell,  the  cardinal 
extremities  rounded,  the  anterior  margin  nearly  straight  or  somewhat 
emarginate  in  its  median  portion,  curving  regularly  into  the  lateral  mar- 
gins at  each  side.  The  dimensions  of  two  individuals  are :  length  of 
pedicle  valve  33  mm.  and  27.5  mm.,  width  38  mm.  and  32.3  mm.,  length 
of  hinge-line  17  mm.  and  17  mm.,  thickness  approximately  9  mm.  and 
7  mm. 

Pedicle  valve  most  convex  at  a  point  about  half  way  between  the  middle 
and  the  beak,  the  surface  curving  more  abruptly  to  the  cardinal  margin, 
very  slightly  or  not  at  all  compressed  towards  the  cardinal  extremities, 


L52  MISSISSIPPI  W    BBACHIOPODA 

sloping  with  a  gently  convex  curvature  to  the  Lateral  and  anterior  mar- 
gins; the  mesial  portion  of  the  valve  scarcely  or  not,  at  all  differentiated 
from  the  general  surface  in  the  umbonal  region,  in  the  median  portion 
of  the  valve  and  towards  the  front  there  is  usually  a  low,  ill-defined, 
rounded,  mesial  fold  bounded  by  much  narrower,  equally  ill-defined,  shal- 
low furrows,  the  top  of  the  fold  not  being  raised  above  the  general  convex 
curvature  of  the  valve,  near  the  front  margin  the  median  portion  of  the 
valve  is  commonly  depressed  to  a  slight  degree  in  a  broad,  shallow,  ill- 
defined  sinus;  the  beak  short  and  a  little  incurved;  cardinal  area  small, 
concavely  curved  from  the  base  to  the  apex,  the  lower,  flattened  portion 
sloping  posteriorly  from  the  plane  of  the  valve  at  an  angle  of  about  40 
degrees,  the  Lateral  margins  sharply  defined,  the  delthyrium  large,  much 
broader  than  high,  its  width  at  the  base  about  one-third,  or  nearly  one- 
ihird,  the  total  length  of  the  hinge-line.  Internally  the  cardinal  teeth 
are  strong  and  diverging,  originating  on  either  side  of  the  delthyrium 
from  the  floor  of  the  valve ;  the  muscular  scars  are  subovate  in  outline 
and  rather  small  for  this  genus,  their  total  length  usually  being  less  than 
one-half  the  length  of  the  valve ;  they  are  rather  deeply  impressed,  with 
a  raised  border,  the  adductor  scars  do  not  reach  anteriorly  as  far  as  the 
diductors  but  in  front  of  them,  a  distinctly  elevated  median  ridge  sepa- 
rates the  two  lobes  of  the  diductor  scars,  the  unpaired  pedicle  muscular 
scar  occupies  the  rostral  portion  of  the  valve  and  is  differentiated  from 
the  contiguous  scars  in  front ;  beyond  the  muscular  scars  the  inner  surface 
of  the  valve  is  pitted  or  is  covered  with  faint,  anastomosing  ridges,  and 
along  the  lateral  and  anterior  margins  it  is  crenulated,  the  crenulations 
corresponding  in  size  with  the  exterior  costse  of  the  valve. 

Brachial  valve  about  equally  convex  with  the  pedicle,  the  greatest 
convexity  a  little  posterior  to  the  middle,  the  surface  sloping  with  a 
gently  convex  curvature  to  the  lateral  and  anterior  margins,  a  little  com- 
pressed towards  the  cardinal  extremities ;  a  shallow,  rounded,  ill-defined 
mesial  sinus  originates  in  the  umbonal  region  and  continues  to  the  anterior 
margin ;  the  beak  small  and  short,  not  incurved ;  cardinal  area  smaller 
than  that  of  the  opposite  valve,  its  surface  lying  in  nearly  the  plane  of 
the  valve.  Internally  the  cardinal  process  is  rather  small  and  low, 
rising  from  the  posterior  extremity  of  a  rather  broad,  elevated  ridge  occu- 
pying the  median  line  of  the  interior  of  the  valve  and  extending  anteriorly 
from  the  apex  of  the  valve  to  an  ill-defined  termination  near  the  anterior 
margins  of  the  muscular  scars ;  socket  plates  strong  and  widely  diverging, 
resting  upon  the  floor  of  the  valve ;  the  muscular  scars  shorter  and  a  little 
wider  than  those  of  the  opposite  valve ;  the  lateral  and  anterior  margins 
of  the  valve  crenulated  internally. 

Surface  of  both  valves  marked  by  numerous,  uniform,  depressed, 
rounded,  radiating  costae,  which  increase  by  bifurcation  and  intercalation. 


RIlIPinoMKI.l.A  153 

about  two  or  three  of  which  occupy  the  space  of  one  millimeter  at  the 
outer  margin  of  a  mature  specimen  of  average  size.  Regular,  concentric 
growth  lines  are  present  upon  both  valves,  sometimes  rather  uniformly 
distributed  but  usually  more  crowded  towards  the  front;  much  finer  con- 
centric lines  may  be  also  detected  upon  some  shells.  The  shell  substance 
is  pierced  by  radiating  canals  or  tubules  of  two  sizes,  following  tbe 
direction  of  the  surface  costa?,  the  larger  ones  apparently  occupy  the 
position  of  the  median  lines  of  the  costa?,  along  the  summits  of  which 
openings  into  the  canals  are  present  at  irregular  intervals,  the  finer  canals 
occupy  the  slopes  of  the  costa?  and  the  intervening  furrows,  and  upon 
slightly  weathered  specimens  their  openings  are  so  numerous  as  to  give  to 
the  shell  a  decided  punctate  appearance. 

Remarks. — As  commonly  preserved  the  shells  of  this  species  are  crushed 
and  often  distorted,  but  a  sufficient  number  of  undistorted  examples, 
mostly  detached  valves,  have  come  under  observation  to  show  all  the 
essential  features  of  the  species.  The  species  is  especially  characterized 
by  its  proportionally  broader  form  and  smaller  muscular  sears  of  the 
pedicle  valve  than  is  usual  in  the  genus,  and  by  the  obscure  and  ill- 
defined  mesial  fold  of  the  pedicle  valve  which  is  bordered  on  either  side 
by  an  obscure  rounded  furrow.  This  latter  character  is  not  of  sufficient 
strength  to  be  preserved  in  the  crushed  examples,  but  in  the  undistorted 
valves  it  seems  always  to  be  present.  The  mesial  sinus  of  the  brachial 
valve  is  much  stronger  than  the  two  furrows  of  the  pedicle  valve,  and  is 
a  much  more  conspicuous  feature  than  in  B.  burlingtonensis,  the  species 
which  this  one  perhaps  most  closely  resembles. 

Horizon.— Kinderhook  (New  Providence  shale,  Kentucky). 

R.HIPIDOMELLA  DIMINUTIVA  Row]ry 

Plate  XX,  Pigs.  9-18,  30-35 

1900.     Rhipidomella  dimmutwa  Rowley,  Am.  Geol.,  vol.  25,  p.  261,  pi.  5, 
figs.   41-43. 

Description.  —  Shell  usually  a  little  below  medium  size,  subovate  in  out- 
line, a  little  longer  than  wide  or  rarely  with  the  length  and  breadth  nearly 
equal,  the  greatest  width  anterior  to  the  middle,  the  hinge-line  from  one- 
third  to  one-half  the  total  width  of  the  shell,  the  cardinal  extremities 
rounded.  The  dimensions  of  three  specimens  are :  length  of  pedicle 
valve  19  mm.,  20  mm.,  and  19.3  mm. ;  length  of  brachial  valve  18  mm., 
19  mm.,  and  18.9  mm. ;  gi-eatest  Avidth  17.4  mm.,  18.8,  and  19  mm. ;  thick- 
ness 8.8  mm.,  10.2  mm.,  and  9  mm.;  length  of  hinge-line  6.5  mm.,  7.5  mm., 
and  6.9  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  cardinal  margin,  more  gently  to  the  lateral  margins  and 
still  more  gently  to  the  anterior  margin,  slightly  compressed  towards  the 
cardinal  extremities;  the  median  portion  of  the  valve  obscurely  flattened 


154  MISSISSIPPI^    BEACHIOPODA 

anteriorly  or  sometimes  with  a  slight,  ill-defined  median  sinus;  the  beak 
small,  a  little  incurved,  extending  posteriorly  only  slightly  beyond  that 
of  the  opposite  valve;  cardinal  area  small,  concave,  with  the  curvature 
increasing  towards  the  beak,  the  inferior,  flatter  portion  sloping  poster- 
iorly at  an  angle  of  from  50  to  60  degrees  to  Hie  plane  of  the  valve,  the 
lateral  margins  sharply  defined  ;  t  he  dell  hyrium  broadly  triangular,  much 
wider  than  high,  its  width  at  the  base  usually  equal  to  about  one-third 
the  total  length  of  the  binge-line.  Internally  the  cardinal  teeth  are  of 
moderate  size  and  are  widely  divergent;  the  muscular  scars  are  large, 
with  their  margin  extending  beyond  the  middle  line  of  the  valve,  flabellate 
in  outline,  the  adductor  scars  occupy  a  central,  subcircular  area,  nearly 
one-third  at'  the  total  length  of  the  entire  scar,  which  is  distinctly  raised 
above  the  general  surface  of  the  valve  anteriorly  and  in  front  of  which  a 
gradually  decreasing  median  ridge  continues  nearly  to  the  limits  of  the 
diductor  scars;  the  unpaired,  median  pedicle  scar  is  very  large,  occupying 
the  entire  rostral  portion  of  the  shell  and  encroaching  upon  the  adjacent 
scars  in  front  from  which  it  is  sharply  differentiated;  the  inner  margin 
of  the  valve  distinctly  crenulate  laterally  and  anteriorly. 

brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  with 
the  greatest  convexity  posterior  to  the  middle,  the  surface  curving  more 
abruptly  to  the  cardinal  margin,  more  gently  to  the  lateral  margins  and 
most  gently  to  the  anterior  margins,  usually  a  little  compressed  towards 
the  cardinal  extremities;  a  shallow,  rounded,  rather  narrow,  ill-defined 
median  sinus  originates  in  the  umbonal  region  and  continues  to  the  an- 
terior margin ;  the  beak  is  inconspicuous,  very  obtusely  pointed  and  not 
incurved  ;  the  cardinal  area  much  smaller  than  that  of  the  opposite  valve, 
lying  in  nearly  the  plane  of  the  valve.  Internally  the  cardinal  process  is 
erect,  rather  prominent,  and  obtusely  pointed  at  the  summit,  the  posterior 
face  is  subcarinate  along  its  median  line,  becoming  obscurely  trilobate 
towards  the  summit,  and  is  nearly  vertical  to  the  plane  of  the  valve,  the 
anterior  face  is  transversely  rounded  and  slopes  rather  abruptly  to  the 
front  and  is  extended  anteriorly  along  the  inner  surface  of  the  valve  as  a 
rounded  median  ridge  which  flattens  out  and  becomes  obsolete  at  the 
anterior  extremity  of  the  muscular  scars ;  from  either  side  of  the  cardinal 
process  the  socket  plates  originate  and  diverge  widely,  from  the  outer 
surface  of  each  one  a  conspicuous  lateral  process  limits  the  dental  sockets, 
but  beyond  these  processes  the  plates  are  produced  into  free,  crura-like 
extensions ;  the  muscular  scars  are  distinctly  quadripartite  and  are  sub- 
quadrangular  in  outline,  their  anterior  margin  reaching  to  about  the 
middle  of  the  valve ;  the  inner  margin  of  the  valve  is  distinctly  crenulate 
anteriorly  and  laterally. 

The  surface  of  each  valve  is  marked  by  fine,  rounded,  radiating  costae, 
three  or  four  of  which  occupy  the  space  of  one  millimeter.     These  costae 


RHIPIDOMELLA  155 

are  neaTly  uniform  in  size  and  increase  by  bifurcation  and  intercalation, 
they  arc  crossed  by  concentric  lines  of  growth  which  vary  in  strength  and 
position  on  different  individuals.  The  shell  substance  is  pierced  by 
radiating  canals  or  tubules  of  two  sizes,  which  follow  the  direction  of  the 
costa\  the  larger  ones  open  at  more  or  less  distant  intervals  along  the 
summits  of  the  costae,  and  openings  of  the  finer  ones  are  closely  crowded 
throughout  the  entire  intervening  space,  giving  to  the  shell  when  in 
proper  condition  of  preservation  a  distinctly  punctate  appearance. 

Remarks. — This  species  differs  from  R.  burlingtonensis  in  its  somewhat 
smaller  size,  its  finer  costa%  its  more  elongate  outline,  and  its  more  distinct 
mesial  sinus  of  the  brachial  valve.  Besides  these  external  differences, 
the  cardinal  process  is  not  so  prominent  as  in  R.  burlingtonensis,  and  the 
socket  plates  are  more  distinctly  produced  into  crura-like  extensions  than 
has  been  observed  in  that  species. 

The  species  occurs  near  the  summit  of  the  Kinderhook  and  base  of  the 
Burlington  limestone,  occurring  rather  commonly  in  the  white  cherts  of 
lower  Burlington  age  at  Louisiana,  Missouri,  which  is  the  type  locality. 
The  species  was  originally  described  by  Rowley  from  immature  specimens 
about  6  mm.  in  length,  the  larger  examples  present  in  the  same  fauna 
being  identified  as  R.  burlingtonensis.  A  careful  examination  of  speci- 
mens corresponding  with  the  type  of  the  species  in  size  and  in  stage  of 
development,  and  also  of  mature  examples,  has  led  the  writer  to  the  con- 
clusion that  the  small  shells  are  certainly  the  young  of  the  larger  ones, 
although  the  smaller  examples  are  proportionally  somewhat  broader  than 
the  mature  ones.  There  seems  to  be,  however,  sufficient  reason  for  the 
separation  of  these  shells  from  R.  burlingtonensis,  and  consequently  the 
name  is",  diminutiva  must  be  extended  to  cover  the  mature  as  well  as  the 
younger  representatives  of  the  species. 

Horizon. — Upper  Kinderhook  and  lower  Burlington  limestone. 

Rhipidomella  thiemei  (White) 

Plate  XXI,  Figs.  8-27 

1880.  Orthis  thii  mei  White,  Contr.  to  Pal.,  No.  8,  p.  164,  pi.  41,  figs.  4a-d. 
1892.     Orthis  Thiemti  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  6A, 

figs.  14-15. 
1901.     Rhipidomella  burlingtonensis  Weller,  Trans.  St.  Louis  Acad.  Sci., 

vol.  11,  p.  181,  pi.  16,  fig.  6. 
1904.     Rhipidomella  thiemei  Girtv,  U.  S.  Geol.  Survey,  Prof.  Paper  No.  21, 

p.  48,  pi.  10,  figs.  1-2. 

Description.— Shell  small,  subquadrate  to  subovate  in  outline,  the  length 
and  width  subequal  or  wider  than  long,  the  hinge-line  much  shorter  than 
the  greatest  width,  the  cardinal  extremities  rounded.  The  dimensions  of 
an  undersized  but  very  complete  specimen  are:  length  of  pedicle  valve 
7.5  mm.,  length  of  brachial  valve  7.4  mm.,  greatest  width  8.4  mm.,  length 


156  Mississil'i'lAX    BRACHIOPODA 

of  hinge-line  5  mm.,  thickness   I.:;  mm.    The  length  of  one  of  the  largest 

pedicle  valves  observed  is  12  nun. 

Pedicle  valve  depressed  convex,  the  median  portion  of  the  valve  broadly 
flattened  from  the  beak  anteriorly,  the  surface  curving  rather  abruptly 
to  i  be  cardinal  margin  and  mucb  more  gently  to  the  lateral  and  anterior 
margins,  very  slightly  or  not  at  all  compressed  towards  the  cardinal 
extremities;  mesial  sinus  originating  near  the  mid-length  of  the  valve 
and  becoming  rapidly  deeper  towards  the  front  where  it  forms  a  rather 
conspicuous  depression  in  the  larger  individuals;  it  is  rounded  in  the 
bottom  and  ill-defined  laterally;  the  beak  is  small,  pointed  and  only 
a  little  incurved;  the  cardinal  area  is  small,  moderately  incurved,  of  mod- 
erate height,  and  is  not  very  sharply  defined  at  its  lateral  margins;  the 
delthyrinm  is  large  and  open  and  occupies  fully  one-half  the  entire  car- 
dinal area.  Internally  the  hinge-teeth  are  rather  large  and  strong,  and 
are  supported  by  very  short  dental  lamella-;  the  flabellate  muscular  scars 
are  large,  reaching  anteriorly  beyond  the  middle  of  the  valve,  sometimes 
extending  four-fifths  the  total  length  of  the  valve,  the  adductor  scars  are 
small,  usually  depressed  below  the  general  surface  posteriorly,  but  ele- 
vated anteriorly  and  extended  to  the  anterior  margin  of  the  diductor 
sears  as  an  elevated  ridge  with  gradually  converging  sides,  the  diductor 
scars  very  large  and  generally  marked  by  radiating  ridges. 

Brachial  valve  a  little  deepter  than  the  pedicle  and  more  regularly  con- 
vex, the  surface  curving  rather  abruptly  to  the  cardinal  margin  and  more 
gently  to  the  lateral  and  anterior  margins,  the  mesial  portion  of  the  valve 
sometimes  slightly  flattened,  but  usually  not  differentiated  from  the  gen- 
eral curvature;  the  beak  small,  obtusely  pointed  and  not  incurved;  the 
cardinal  area  very  small  and  lying  in  nearly  the  plane  of  the  valve.  In- 
ternally the  cardinal  process  is  large,  its  posterior  surface  is  divided  by  a 
median  ridge  which  slopes  from  the  highest  point  towards  the  beak,  the 
anterior  surface  drops  nearly  vertically  to  the  floor  of  the  valve,  along 
which  the  process  is  continued  as  a  median  ridge  of  greater  or  less  strength 
to  about  the  middle  of  the  valve ;  the  dental  sockets  are  large  and  deep, 
the  socket-plates  are  prominent  and  are  produced  anteriorly  into  slightly 
divergent,  crura-like  processes;  the  muscular  scars  are  quadripartite, 
being  smaller  and  much  less  deeply  impressed  than  those  in  the  pedicle 
valve. 

The  surface  of  both  valves  marked  by  fine,  rounded,  radiating  costae 
which  increase  by  bifurcation,  from  four  to  five  occupying  the  space  of 
one  millimeter.  More  or  less  inconspicuous,  concentric  lines  of  growth 
are  also  usually  present. 

Remarks. — This  is  one  of  the  smaller  species  of  the  genus,  being  com- 
parable in  size  to  R  dubia.  and  R.  jfrseyensis  only.  It  differs  from  R. 
jerscyensis,  with  which  it  is  similar  in  general  form,  in  the  conspicuous 
mesial  flattening  of  the  pedicle  valve,  and  the  well  developed  mesial  sinus 


RJIIPIDOMELLA  157 

in  the  anterior  portion  of  the  same  valve,  as  well  as  in  the  absence  of 
the  mlesial  sinus  of  the  brachial  valve.  From  B.  dubia  it  differs  in  its 
longer  hinge-line  and  larger  cardinal  area,  and  in  its  more  quadrangular 
outline. 

Horizon. — Upper  Kinderhook. 

KlIIIMDOMELIA  JERSEYENSIS  n.  Sp. 

Plate  XX,  Figs.  36-43 

1909.  Ehipxhrm,  II a  michelinia  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  295, 
pi.  12,  figs.  8-10. 

Description.  —  Shell  small,  wider  than  long,  broadly  subovate,  frequently 
emarginate  in  front,  the  greatest  width  anterior  to  the  middle,  the  hinge- 
line  less  than  one-half  the  greatest  width  of  the  shell,  the  cardinal  ex- 
tremities rounded.  The  dimensions  of  a  nearly  complete  specimen  of  av- 
erage size  are :  length  of  pedicle  valve  14  mm.,  length  of  brachial  valve  13 
mm.,  maximum  width  15  mm.,  length  of  hinge-line  6.5  mm.,  thickness 
6.7  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  cardinal  margin  and  more  gently  to  the  lateral  and  ante- 
rior margins,  the  cardinal  extremities  usually  somewhat  compressed ;  the 
median  portion  of  the  valve  marked  by  an  obscure,  broadly  rounded  fold 
which  is  not  defined  laterally  and  which  frequently  becomes  flattened  out 
and  obsolete  anteriorly  ;  the  beak  small,  extending  posteriorly  only  a 
short  distance  beyond  the  hinge-line ;  the  cardinal  area  small,  nearly  flat 
or  gently  concave,  its  lateral  margins  sharply  defined,  sloping  posteriorly 
at  an  angle  of  30  degrees  or  less  to  the  plane  of  the  valve ;  the  delthyrium 
large,  broadly  triangular,  its  width  along  the  base  being  about  one-third 
the  total  length  of  the  hinge-line.  Internally  the  cardinal  teeth  are  of 
moderate  strength  and  rather  widely  divergent ;  the  muscular  scars  are  of 
moderate  size,  extending  anteriorly  less  than  one-half  the  length  of  the 
shell  from  the  beak,  and  are  only  slightly  depressed  below  the  general 
internal  surface  of  the  valve;  the  lateral  and  anterior  margins  crenulate 
internally. 

Brachial  valve  nearly  equally  convex  with  the  pedicle,  its  greatest  con- 
vexity near  or  posterior  to  the  middle,  the  surface  sloping  with  a  gently 
convex  curvature  in  all  directions,  the  cardinal  extremities  often  a  little 
compressed ;  the  median  portion  of  the  valve  marked  by  a  distinct  hut 
shallow,  rounded,  median  sinus,  originating  in  the  umbonal  region  and 
becoming  stronger  anteriorly,  not  sharply  defined  laterally;  the  beak 
small,  not  incurved ;  the  cardinal  area  almost  obsolete,  lying  in  the  plane 
of  the  valve.  Internally  the  dental  plates  are  rather  prominent  and 
widely  divergent ;  the  cardinal  process  is  very  small,  rising  slightly  from 
the  posterior  extremity  of  a  rather  broad,  low,  median  ridge  which  ex- 
tends anteriorly  along  the  floor  of  the  valve  to  the  anterior  margin  of  the 


158  .  M  isslssilTi  w    BRACHIOPODA 

muscular  scars;  muscular  scars  rather  faint,  their  anterior  margin  nol 
reaching  to  the  middle  of  the  valve,  obscurely  quadripartite;  the  lateral 
and  anterior  margins  crenulate  anteriorly. 

Surface   of   both    valves    marked    by    fine,   depressed,   radiating   costse, 

about  four  or  five  of  which  occupy  millimeter  along  the  front  margin 

of  an  average  size  specimen.  The  costiu  increase  by  bifurcation  and  inter- 
calation and  remain  nearly  uniform  in  size.  Crossing  the  costa>  upon  well 
preserved  shells  there  are  exceedingly  fine  concentric  lines,  and  stronger, 
more  or  less  irregularly  distributed  concentric  lines  of  growth.  The  shell 
substance  is  pierced  by  radiating  tubules  which  follow  the  direction  of 
the  costse,  with  openings  at  intervals  along  the  summits  of  the  costas. 
Finer  tubules,  such  as  are  present,  in  I!,  burlvngtonensis,  have  not  been 
observed,  although  they  may  be  present. 

Remarks.  This  species  occurs  in  great  numbers  in  the  Fern  Glen  Kin- 
derhook  of  Illinois  and  .Missouri.  It  is  characterized  by  its  exceedingly 
fine  costse,  by  the  distinct  mesial  sinus  of  the  brachial  valve,  by  the  po- 
sition of  the  cardinal  area  of  the  pedicle  valve  which  slopes  posteriorly 
more  nearly  in  the  plane  of  1  he  valve  than  in  any  other  of  the  species  here 
described,  and  in  the  small  size  of  the  cardinal  process.  By  one  or  more 
of  the  above  characters  the  species  may  be  distinguished  from  any  of  the 

other  species. 

In  its  typical  expression  this  species  is  a  small  form,  but  associated  with 
it  are  a  smaller  number  of  a  much  larger  shell  approaching  F.  burlington- 
i  //sis  iii  size  and  form.  The  smaller  specimens  have  usually  been  con- 
sidered as  being  the  immature  examples  of  the  larger  form,  but  many  of 
the  small  individuals  give  every  evidence  of  being  fully  mature,  and  it  is 
more  than  probable  that  two  species  are  represented.  The  larger  one 
does  not  exhibit  the  distinct  mesial  sinus  of  the  brachial  valve  which  is 
such  a  marked  characteristic  of  the  smaller  one,  the  cardinal  area  of  the 
pedicle  valve  does  not  lie  quite  so  near  the  plane  of  the  valve,  the  cardinal 
process  is  more  prominent  and  the  muscular  impressions  are  somewhat 
larger.  Most  of  these  characters,  however,  except  the  sinus  of  the  brachial 
valve  which  ought  to  persist,  might  be  due  to  the  greater  age  of  the  larger 
shells. 

Horizon.  —  Fern  Glen  formation. 

Rhipidomella  tenuicostata  n.  sp. 
Plate  XX,  Figs.  27-29 

Description. — Shell  small,  lenticular  in  form,  subovate  in  outline,  vary- 
ing from  longer  than  wide  to  wider  than  long,  the  greatest  width  anterior 
to  the  middle,  the  hinge-line  short,  usually  not  exceeding  one-third  the 
width  of  the  shell,  the  cardinal  extremities  rounded.  The  dimensions  of 
two  nearly  perfect  specimens  are:  length  of  pedicle  valve  15.3  mm.  and 


RHIPIDOMELDA  159 

10.2  mm.,  length  of  brachial  valve  14.6  mm.  and  9.9  mm.,  maximum  width 
16  mm.  and  10  mm.,  length  of  hinge  line  5  mm.  and  3.2  mm.,  thickness  6.7 
mm.  and  4.8  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle  near  the  umbonal 
region,  the  surface  curving  abruptly  to  the  cardinal  margin  and  gently 
to  the  lateral  and  anterior  margins,  usually  a  little  compressed  towards 
the  cardinal  extremities;  the  mesial  portion  of  the  valve  usually  not  dif- 
ferentiated from  the  general  curvature  of  the  surface ;  the  beak  small,  a 
little  incurved ;  the  cardinal  area  very  small,  sloping  posteriorly  in  an 
angle  not  exceeding  25  degrees  to  the  plane  of  the  valve,  sometimes  ap- 
parently lying  almost  in  the  plane  of  the  valve;  the  delthyrium  large, 
broadly  triangular,  its  width  along  the  base  more  than  one-third  the  total 
length  of  the  hinge-line.  Internally  the  hinge-teeth  are  of  moderate  size 
and  are  widely  divergent ;  the  characters  of  the  muscular  scars  have  not 
been  satisfactorily  determined,  but  they  do  not  extend  anteriorly  beyond 
the  middle  of  the  valve;  the  inner  margins  are  crenulate  anteriorly  and 
laterally. 

Brachial  valve  about  equally  convex  with  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  the  surface  curving  to  the  margins  rather  gently 
in  all  directions,  the  cardinal  extremities  sometimes  a  little  compressed ; 
the  mesial  portion  of  the  valve  either  not  differentiated  from  the  general 
curvature  of  the  surface  or  depressed  in  a  slight  mesial  sinus  which  is 
narrow,  shallow  and  ill  defined  laterally;  the  beak  shorter  and  more  ob- 
tusely pointed  than  that  of  the  opposite  valve,  not  incurved;  the  cardinal 
area  very  small,  lying  in  nearly  the  plane  of  the  valve.  Internally  the 
cardinal  process  is  large  and  strong,  its  posterior  face  transversely  convex 
and  sloping  posteriorly  from  the  summit  at  an  angle  of  about  45  degrees 
to  the  plane  of  the  valve,  anteriorly  it  is  continued  along  the  median  line 
of  the  inner  surface  of  the  valve  as  a  conspicuous,  broad,  rounded  ridge 
which  reaches  to  about  the  middle  of  the  valve ;  the  socket  plates  flank 
the  cardinal  process  on  either  side,  and  are  abruptly  bent  to  an  anterior 
direction,  and  for  the  greater  part  of  their  length  they  are  parallel  with 
each  other  and  with  the  median  line  of  the  valve ;  the  characters  of  the 
muscular  scars  have  not  been  clearly  determined. 

The  surface  of  each  valve  is  marked  by  exceedingly  fine,  nearly  uni- 
form, radiating  costa*  which  increase  by  bifurcation  and  intercalation, 
about  four  or  five  occxipying  the  space  of  one  millimeter.  The  costs?  are 
crossed  by  concentric  lines  of  growth  of  moderate  strength,  varying  in 
number  and  distribution  upon  different  individuals.  The  shell  substance 
is  apparently  perforated  by  radiating  canals  or  tubules  following  the  di- 
rection of  the  costa*,  which  open  at  intervals  along  the  summits  of  the 
costse ;  the  presence  of  finer  tubules  in  the  intervening  spaces  is  not  clearly 
shown  in  any  of  the  examples  studied. 


160  MISSISSIITIAN    BBACHIOPODA 

Remarks.  In  its  amal]  adze  and  fine  costte,  this  species  agrees  most 
closely  with  /,'.  jerseyensis,  bul  it  differs  externally  from  that  species  in 
being  proportionally  more  elongate  and  in  the  entire  absence  or  very 
slighl  developmenl  of  a  mesial  sinus  in  Ihe  brachial  valve.  Internally 
this  species  is  totally  different  from  /.'.  jerseyensis  in  the  characters  of 
the  cardinal  process  and  socket  plates,  the  cardinal  process  being  exceed- 
ingly large  and  prominent,  while  in  that  species  it.  is  small.  The  median 
ridge  along  the  inner  surface  of  the  brachial  valve  is  much  more  strongly 
developed  than  in  any  other  member  of  the  genus  here  described. 

Horizon.    Chouteau  limestone. 

K.IIII'JINIMKLLA   DUBIA    (Hall) 

Plate  XX,  Figs.  22-26;  Plate  LXXXIII,  Figs.  9-10 

1856.     Orthis  dubia  Hall,  Trans.  Albany  Inst...  vol.  4,  p.  12. 
1863.     Orthis   Cooperensis   Swallow,    Trans.    St.    Louis   Acad.   Sci.,   vol.   2, 
p.   82. 

1882.  Orthis  dubia  Whitfield,  Bull.  Am.  Mus.  Mat,  Hist.,  vol.  1,  p.  45, 

pi.  6,  figs.  !-.">. 

1883.  Orthis  dubia  Hall,  12th  Ann.  Hep.  Geol.  Surv.  Ind.,  p.  324,  pi.  29, 

figs.  1-5. 
1892.     Orthis  dubia  Hall  and  Clarke.  Int.  to  Study  of  Braeh.,  pt.  1,  pi.  12, 

figs.  10-13. 
1892.     Orthis  dubia  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt    1,  pi.  6A, 

figs.  18-22. 
1894.     Orthis  dubia  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  64. 
1906.     Rhipidomella   dubia  Beede,  30th.  Ann.   Rep.   Geol.   Surv.   Ind.,   p. 

1303,  pi.  22,  figs.  1-4. 

Description.  —  Shell  small,  usually  a  little  longer  than  wide,  subovate  in 
outline,  the  greatest  width  usually  anterior  to  the  middle,  the  anterior 
margin  nearly  straight  or  slightly  convex  in  the  middle,  sometimes 
slightly  emarginate,  the  antero-lateral  margins  regularly  rounded,  the 
postero-lateral  margins  gently  convex,  becoming  straighter  as  they  ap- 
proach the  beak  where  they  meet  usually  in  an  angle  a  little  less  than  a 
right  angle,  the  hinge-line  very  short ;  the  twro  valves  subequally  convex. 
The  dimensions  of  two  individuals  are :  length  of  pedicle  valve  14  mm. 
and  11.7  mm.,  length  of  brachial  valve  13  mm.  and  11  mm.,  greatest  width 
13.7  mm  and  11.9  mm.,  thickness  8  mm.  and  6.6  mm. 

Pedicle  valve  flattened  medially  in  its  posterior  half,  the  surface  curv- 
ing abruptly  to  the  posterio-lateral  margins,  often  with  a  slight  incurva- 
ture to  the  cardinal  extremities,  and  curving  gently  to  the  anterior  and 
antero-lateral  margins ;  mesial  sinus  rather  broad  and  rather  shallow, 
originating  in  or  near  the  umbonal  region,  its  lateral  boundaries  ill- 
defined,  sometimes  rather  abruptly  deepened  as  it  approaches  the  anterior 
margin;  the  beak  compressed,  slightly  or  only  moderately  incurved;  car- 


SCHIZOPHORIA  161 

dinal  area  obsolete,  the  delthyrium  rather  large,  about  as  wide  or  wider 
than  high.  Internally  the  hinge-teeth  are  large  and  strong,  the  muscular 
impressions  large,  flabellate,  deeply  impressed  and  usually  extending  two- 
thirds  the  length  of  the  valve  from  the  beak,  the  central  or  adductor  im- 
pressions are  situated  upon  a  narrow,  raised,  median  ridge ;  the  anterior 
margin  of  the  valve  finely  crenulated  internally. 

Brachial  valve  more  rotund  than  the  pedicle,  with  its  greatest  convex- 
ity near  the  middle  or  a  little  posterior  to  the  middle,  from  which  point 
the  surface  curves  to  the  margins  in  all  directions,  the  curvature  being  a 
little  more  abrupt  to  the  posterolateral  margins ;  the  mesial  fold  scarcely 
differentiated  from  the  general  convexity  of  the  valve  except  sometimes 
near  the  anterior  margin  ;  the  beak  pointed  and  slightly  incurved.  In- 
ternally the  cardinal  process  is  large  and  strong,  sometimes  extending 
anteriorly  from  the  beak  for  one-fourth  the  length  of  the  valve ;  the  mus- 
cular scars  less  deeply  impressed  than  those  of  the  opposite  valve,  divided 
along  the  median  line  by  a  narrow,  elevated  ridge ;  the  anterior  margin  of 
the  valve  finely  crenulate  interiorly. 

The  surface  of  both  valves  marked  by  exceedingly  fine  radiating  costse, 
about  three  of  which  occupy  the  space  of  one  millimeter  at  the  front 
margin  of  a  mature  shell,  these  costaa  are  commonly  worn  away  from  the 
greater  portion  of  the  valves  so  that  their  surface  appears  to  be  nearly  or 
quite  smooth,  but  they  may  usually  be  detected  in  the  mesial  sinus  near 
the  front  of  the  pedicle  valve  where  the  surface  is  more  protected  than 
elsewhere. 

Remarks.— This  species  is  a  well-marked  form,  characterized  by  its 
small  size,  its  short  hinge-line  and  especially  by  the  obsolete  cardinal  area, 
the  marked  flattening  of  the  posterior  portion  of  the  pedicle  valve  and 
the  more  deeply  depressed  sinus  near  the  front  of  the  same  valve  than  is 
common  in  the  genus.  The  size  of  the  species  rarely  exceeds  that  of  the 
larger  individual  whose  dimensions  are  given  above,  although  the  largest 
specimen  observed  has  a  length  of  17  mm.  and  a  width  of  17.8  mm.  The 
average  size  of  the  species  is  not  far  from  that  of  the  smaller  example 
whose  dimensions  are  given. 

Horizon. — Keokuk  limestone,  "Warsaw  formation  and  Salem  limestone. 

Genus  SCHIZOPHORIA  King 

Description. — Shell  subcircular  or  subelliptical  in  outline,  resupinate 
or  with  the  valves  subequally  convex.  Hinge-line  shorter  than  the  great- 
est width  of  the  shell,  the  cardinal  areas  rather  low.  The  pedicle  valve 
with  short  dental  plates  which  are  continued  as  rather  sharp  ridges  along 
the  floor  of  the  valve  bounding  the  muscular  area.  The  muscular  scars 
of  the  pedicle  valve  less  than  half  the  length  of  the  valve,  obcordate  or 
subovate  in  outline,  more  or  less  deeply  impressed  in  the  substance  of  the 

—6 


162 


MISSISSIPPIAN    BR  xciliol'ODA 


valve  mid  bordered  by  elevated  margins,  divided  longitudinally  by  an 
elevated  ridge  upon  which  are  situated  the  adductor  scars.  In  the  brachial 
valve  the  sockel  plates  arc  ered  and  divergent;  the  cardinal  process  is 
similar  to  that  of  Rhipidomella  bul  becomes  resorbed  and  narrowed  with 
age  .  the  muscular  scars  are  quadripartite  and  much  less  distinctly  defined 
than  those  of  the  pedicle  valve.  Surface  of  both  valves  marked  by  fine, 
hollow,  tubulose  COStffi,  which  are  produced  into  short  spines  as  in 
Rhipidomella. 

Schizophoeu  subelliptica    (White  and  Whitfield) 
Plate  XXIII,  Figs.  1-5 

1862.     Ortlns  subelliptica  White  and  Whitfield,  Proc.  Bost.  Soc.  Nat.  Hist., 

vol.  8,  p.  292. 
1870.     Orthis  subeTMpticaf  Winchell,  Proc.  Am.  Phil.  Soc,  vol.  11,  p.  251. 
1901.     Sckizopkoria  subelliptica  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol. 

11,  p.  182,  pi.  1(1,  figs.  4-5;  p.  196,  pi.  19,  figs.  6-7. 

Description.—  Shell  small,  broader  than  long,  transversely  subelliptical 
in  outline,  the  greatest  width  near  the  mid-length  of  the  shell,  the  hinge- 
line  about  two-thirds  the  greatest  width  of  the  shell,  the  cardinal  ex- 
tremities rounded.  The  dimensions  of  two  pedicle  valves  are:  length 
10.8  mm.  and  11  mm.,  width  13.5  mm  and  13.8  mm.,  length  of  hinge-lino 
9  mm.  and  9  mm.,  convexity  3.9  mm  and  3.9  mm. 

Pedicle  valve  most  prominent  on  the  umbo,  curving  abruptly  to  the 
cardinal  margin  and  gently  to  the  anterior  and  antero-lateral  margins, 
compressed  towards  the  cardinal  extremities ;  the  mesial  portion  of  the 
valve  distinctly  flattened  anteriorly  and  usually  depressed  in  an  ex- 
ceedingly shallow,  rather  broad  and  ill-defined  sinus;  the  beak  pointed, 
rather  prominent,  a  little  incurved;  cardinal  area  of  moderate  size,  con- 
cave, the  curvature  increasing  towards  the  beak,  the  lower,  flatter  portion 
lying  at  nearly  a  right  angle  to  the  plane  of  the  valve,  its  lateral  margins 
sharply  defined.     Internal  characters  not  observed. 

Brachial  valve  not  observed. 

Surface  marked  by  fine,  rounded,  radiating  costae,  increasing  by  bifur- 
cation and  intercalation,  every  second  or  third  one  of  which  is  slightly 
larger,  about  four  or  five  occupying  the  space  of  one  millimeter  at  the 
front  of  a  mature  shell  11  mm.  in  length.  The  shell  substance  pierced  by 
radiating  canals  or  tubules  which  follow  the  direction  of  the  costa?,  along 
the  summits  of  the  larger  of  which,  the  canals  open  at  irregular  intervals. 
Crossing  the  radiating  costae  are  regular,  concentric  lines  of  growth, 
usually  obscure  or  obsolete  except  near  the  margin  where  several  are 
crowded  together. 

Remarks. — In  its  typical  expression  this  species  has  been  recognized 
only  in  the  fauna  of  the  Kinderhook    oolite  bed  at  Burlington,  Iowa, 


SCHIZOPHuRIA  163 

although  the  cotypes  of  the  species  include  specimens  from  the  superjacent 
bed  at  the  same  locality.  These  latter  specimens,  however,  grow  to  a 
much  larger  size,  besides  differing  in  some  other  respects,  and  should 
possibly  be  referred  to  the  species  here  described  as  S.  chouteauensis.  In 
some  respects  S.  subelliptica  suggests  a  diminutive  8.  swallovi,  but  the 
surface  of  the  pedicle  valve  is  much  less  flat  than  that  species,  with  the 
beak  and  umbo  proportionally  more  prominent.  The  radiating  costas  are 
also  less  nearly  uniform  in  size  in  this  species,  with  the  external  openings 
of  the  radiating  canals  restricted  to  the  larger  costaj.  The  brachial  valve 
has  not  been  available  for  study,  but  it  is  believed  that  it  much  more 
nearly  equals  the  pedicle  valve  in  convexity  than  in  8.  swallovi,  in  which 
species  the  convexity  of  the  brachial  valve  greatly  exceeds  that  of  the 
pedicle. 

Horizon,— Kinderhook. 

SCHIZOPHORIA    CHOUTEAUENSIS    11.    sp. 

Plate  XXIII,  Figs.  6-19 

Description.  —  Shell  of  medium  size  or  smaller,  broader  than  long,  trans- 
versely subelliptical  in  outline,  the  greatest  width  near  the  mid-length 
of  the  shell,  the  cardinal  extremities  rounded.  The  dimensions  of  two 
nearly  perfect  individuals  are :  length  of  pedicle  valve  19.9  mm.  and 
12  mm.,  length  of  brachial  valve  19  mm.  and  11.8  mm.,  greatest  width 
22.8  mm.  and  14.2  mm.,  length  of  hinge-line  14.4  mm.  and  10  mm.,  thick- 
ness 11.2  mm.  and  7  mm. 

Pedicle  valve  most  convex  near  the  umbo,  the  surface  curving  rather 
abruptly  to  the  cardinal  margin  and  more  gently  to  the  lateral  and 
anterior  margins,  a  little  compressed  towards  the  cardinal  extremities ; 
mesial  sinus  entirety  obsolete ;  umbo  prominent  with  the  beak  rather 
small  and  a  little  incurved ;  the  cardinal  area  small,  its  lateral  margins 
well  defined,  concave  with  the  curvature  increasing  towards  the  beak  the 
lower  and  flatter  portion  lying  at  nearly  a  right  angle  to  the  plane  of  the 
valve.  Internally  the  cardinal  teeth  are  supported  by  short  dental  lamellae 
which  continue  anteriorly  along  the  inner  surface  of  the  valve  as  raised 
ridges  bounding  the  muscular  scars  laterally ;  the  muscle  scars  fall  short 
of  reaching  the  middle  of  the  valves  anteriorly,  they  are  subcordate  in 
outline  with  a  dee]),  acutely  angular  emargination  in  front,  and  are 
divided  longitudinally  by  a  raised,  subangular  ridge,  which  is  highest 
anteriorly  at  the  base  of  the  emargination  and  is  rather  rapidly  reduced 
in  height  posteriorly. 

Brachial  valve  a  little  more  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  surface  curving  abruptly  to  the  car- 
dinal margin  and  more  gently  to  the  lateral  and  anterior  margins,  com- 
pressed towards  the  cardinal  extremities;  the  mesial  portion  of  the  valve 


]()4  MISSISSIPPI^    BBACHIOPODA 

slightly  flattened  1ml  not  differentiated  from  the  general  curvature  of 
the  surface;  beak  smaller  than  that  of  the  opposite  valve  and  a  little 
more  incurved,  projecting  posteriorly  beyond  the  cardinal  line  nearly  as 
far  as  that  of  the  pedicle  valve;  cardinal  area  much  .smaller  than  that  of 
the  opposite  valve,  lying  in  nearly  the  plane  of  the  valve.  Internal 
characters  not  observed. 

Surface  of  both  valves  marked  by  fine,  rounded,  radiating  costa-  of 
nearly  uniform  size,  which  increase  by  bifurcation  and  intercalation,  from 
three  to  lour  of  which  occupy  the  space  of  one  millimeter  at  the  front  of 
n  specimen  about  20  mm.  in  Length;  crossing  the  radiating  costa;  there 
are  regular  concentric  lines  of  growth  which  commonly  become  stronger 
and  more  crowded  towards  the  front.  The  shell  substance  is  pierced  by 
radiating  canals  or  tubules  which  follow  the  direction  of  the  costse,  along 
the  top  of  which  they  open  at  intervals. 

Remarks.— This  species  resembles  S.  subelliptica  but,  besides  being 
larger,  it  lacks  the  distinct  mesial  flattening  of  the  pedicle  valve  and  the 
slight  depression  near  the  front  margin.  On  comparing  examples  of 
this  species  which  correspond  in  size  with  mature  specimens  of  S. 
subelliptica,  the  cost*  are  considerably  finer,  there  being  as  many  as  five 
in  the  space  of  one  millimeter  in  an  example  12  mm.  in  length  at  its 
front  margin.  The  species  differs  from  8.  swallovi  in  its  much  smaller 
size,  in  the  absence  of  the  distinct  flattening  of  the  pedicle  valve  and  in 
the  more  nearly  equal  convexity  of  the  two  valves. 

Horizon.  —  Chouteau  limestone  of  the  Kinderhook. 

SCIIIZOPHORIA  SEDALIENSIS  n.  Sp. 

Plate  XXI,  Figs.  28-32 

Description. — Shell  above  medium)  size,  broader  than  long,  subelliptieal 
in  outline,  the  greatest  width  near  the  mid-length,  hinge-line  shorter  than 
the  greatest  width,  cardinal  extremities  rounded.  The  dimensions  of  a 
nearly  complete  individual  are :  length  of  pedicle  valve  30.5  mm.,  length 
of  brachial  valve  30  mm.,  greatest  width  36  mm.,  length  of  hinge-line  22 
mm.,  thickness  17.8  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbo  a  little 
depressed,  the  surface  curving  abruptly  to  the  cardinal  margin  and  gently 
to  the  lateral  and  anterior  margins,  somewhat  compressed  towards  the 
cardinal  extremities ;  mesial  portion  of  the  valve  broadly  flattened 
towards  the  anterior  margin;  beak  small,  a  little  incurved;  cardinal  area 
small,  sharply  defined  along  its  lateral  margins,  concave,  with  the  curva- 
ture increasing  towards  the  beak;  the  delthyrium  broadly  triangular. 
Internally  the  cardinal  teeth  are  supported  by  short  dental  plates  which 
are  continued  as  low,  angular  ridges  along  the  lateral  margins  of  the 
muscular  scars;  muscular  scars  subovate  in  outline,  less  than  one-half  the 


SCHIZOPIIORIA  165 

length  of  the  valve,  not  emarginate  in  front,  divided  longitudinally  along 
the  median  line  by  an  abruptly  elevated  angular  ridge  which  is  highest 
near  the  front  and  is  gradually  reduced  in  height  towards  the  beak,  in 
front  of  the  muscular  scar  the  median  ridge  is  produced  antei'iorly  as 
a  flattened  rib  upon  the  inner  surface  of  the  valve. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  curving  abruptly  to  the  cardinal 
margin  and  more  gently  to  the  lateral  and  anterior  margins,  compressed 
towards  the  cardinal  extremities ;  the  median  portion  of  the  valve  either 
not  differentiated  from  the  general  curvature  of  the  surface  or  broadly 
and  indefinitely  flattened  from  the  umbonal  region  to  the  front;  the  umbo 
a  little  produced  beyond  the  cardinal  margin,  the  beak  small  and  in- 
curved ;  the  cardinal  area  small,  lying  in  nearly  the  plane  of  the  valve. 
Internally  the  socket  plates  are  prominent  and  widely  divergent,  the 
cardinal  process  is  small,  and  is  not  produced  as  a  median  rib  along  the 
median  line  of  the  inner  surface  of  the  valve ;  the  muscular  scars  are 
subovate  in  outline  and  are  about  equal  in  size  to  those  of  the  opposite 
valve. 

Surface  of  both  valves  marked  by  fine,  radiating,  rounded  costre  which 
increase  by  bifurcation  and  intercalation,  and  about  three  of  which  occupy 
the  space  of  one  millimeter  near  the  front  of  a  mature  example.  The 
costce  are  crossed  by  a  few  more  or  less  indistinct,  concentric  lines  of 
growth.     The  tubular  nature  of  the  costse  has  not  been  obsexwed. 

Remarks. — This  species  most  closely  approaches  S.  swallovi  in  its  char- 
acteristics, but  it  differs  from  that  species  in  the  more  convex  pedicle 
valve  and  in  the  more  nearly  equal  convexity  of  the  two  valves.  In- 
ternally the  shape  of  the  muscular  scars  of  the  pedicle  valve  differs  from 
those  of  S.  swallovi  in  being  without  the  emargination  in  front,  and 
in  having  the  median  septum  which  divides  the  muscular  scar  longi- 
tudinally, produced  anteriorly  as  a  depressed  ridge.  In  general  contour 
the  species  most  closely  resembles  8.  cliouteauensis,  but  it  is  larger  than 
that  species  and  has  the  pedicle  valve  indefinitely  flattened  towards  the 
front,  besides  having  the  same  difference  in  the  form  of  the  muscular 
scar  of  the  pedicle  valve  as  between  it  and  8.  swallovi. 

Horizon.— Upper   Chouteau   limestone. 

SCHIZOPIIORIA  POSTSTBIATULA  n.  sp. 

Plate  XXII,  Figs.  7-14  (H5-17) 

1909.     Schizophoria  sivallovi  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  296, 
pi.  12,  figs.  6-7. 

Description.— Shell  resupinate,  above  medium  size,  wider  than  long, 
subelliptical  in  outline,  the  greatest  width  near  the  mid-length  of  the 


inii  MISSISSll'I'IAN    UKACHIOPODA 

shell,  tlic  hinge-line  a  little  more  than  one-half  the  width  of  the  shell, 
the  cardinal  extremities  rounded.  The  dimensions  of  a  nearly  complete, 
somewhat  crushed  specimen,  are:  length  of  pedicle  valve  approximately 
30  mm..  Length  of  hrachial  valve  approximately  30  mm.,  greatest  width 
36.5  mm.,  Length  of  hinge-line  20  mm.,  thickness  23  mm.,  convexity  of 
pediele  valve  8.2  nun.,  height  of  cardinal  area  4  mm.  The  dimensions  of 
another  nearly  perfeel  hut  somewhat  unsymnietrical  specimen  are :  length 
of  pediele  valve  28  mm.,  length  of  brachial  valve  28.3  mm.,  greatest  width 
32.1   mm.,  thickness  19.2  mm  ,  length  of  hinge-line  18.5  mm. 

Pedicle  valve  much  less  convex  than  the  brachial,  most  prominent  on 
the  umbo,  the  surface  sloping  rather  abruptly  to  the  cardinal  margin, 
and  more  gently  to  the  Lateral  and  anterolateral  margins,  compressed 
towards  the  cardinal  extremities;  the  mesial  portion  of  the  valve  slightly 
flattened  in  the  posterior  portion,  becoming  impressed  anteriorly  in  a 
distinct,  rounded  mesial  sinus  of  moderate  depth;  the  beak  moderately 
prominent  and  a  little  incurved;  cardinal  area  of  moderate  size,  its  lateral 
margins  well  defined,  its  surface  concave  with  the  curvature  increasing 
towards  the  beak,  the  lower  flattened  portion  with  a  slight  posterior  slope 
from  the  hinge-line;  the  delthyrium  of  moderate  size,  about  as  wide  as  high. 
Internally  the  cardinal  teeth  are  supported  by  short  dental  lamella?  which 
are  continued  anteriorly  along  the  inner  surface  of  the  valve  as  elevated 
ridges  along  the  lateral  margins  of  the  muscular  scar;  muscular  scar 
subcordate  in  outline  with  an  angular  emargination  in  front,  less  than 
one-half  the  total  length  of  the  valve,  divided  longitudinally  by  a  strong, 
subangular,  median  ridge  which  is  highest  in  front  opposite  the  emargina- 
tion of  the  muscular  region,  gradually  decreasing  in  prominence  pos- 
teriorly. 

The  brachial  valve  much  more  strongly  convex  than  the  pedicle,  most 
prominent  near  the  middle,  the  surface  curving  abruptly  to  the  margin 
in  all  directions,  slightly  compressed  towards  the  cardinal  extremities, 
the  umbo  prominent  and  projecting  conspicuously  backward  beyond  the 
hinge-line ;  the  mesial  portion  of  the  valve  slightly  differentiated  an- 
teriorly in  a  low,  rounded,  ill-defined  mesial  fold ;  beak  pointed,  much 
more  strongly  incurved  than  that  of  the  opposite  valve ;  cardinal  area 
about  one-half  as  wide  as  that  of  the  pedicle  valve,  concave,  its  lateral 
margins  sharply  defined,  its  inferior  portion  lying  in  nearly  the  plane  of 
the  valve  and  towards  the  apex  curving  towards  the  beak  of  the  opposite 
valve.    Internal  characters  not  observed. 

Surface  of  each  valve  marked  by  fine,  rounded,  nearly  uniform,  radiat- 
ing costae  which  increase  by  bifurcation  and  intercalation,  about  three 
costas  occupy  the  space  of  one  millimeter,  the  intervening  furrows  about 
equaling  the  costse  in  width  ;  crossing  the  radiating  costre  there  are  numer- 
ous, regular,  concentric  lines  of  growth  which  become  stronger  and  more 


SCHIZOPHORIA  167 

crowded  anteriorly  where  they  are  sometimes  subimbricating.  The  shell 
substance  is  pierced  by  radiating  canals  or  tubules  which  open  at  intervals 
alone  the  summits  of  the  costse. 

Remarks. — This  species  has  commonly  been  included  in  S.  sivallovi,  but 
besides  occurring  at  a  lower  horizon  it  possesses  well-marked  distinguish- 
ing characters.  It  never  attains  so  great  a  size  as  S.  sivallovi,  its  pedicle 
valve  is  never  so  flat,  it  possesses  a  distinct  mesial  sinus  toward  the  front 
of  the  pedicle  valve,  and  instead  of  a  slight  mesial  depression  towards 
the  front  of  the  brachial  valve  there  is  a  tendency  towards  a  slight  ele- 
vation or  fold.  In  all  these  characters  the  species  approaches  the  De- 
vonion  8.  stria  tula,  and  it  is  essentially  a  form  intermediate  in  character 
between  this  species  and  S.  swullovi. 

Horizon.— Fern  Glen  formation. 

SCHIZOPHORIA  SWALLOVI    (Hall) 

Plate  XXII,  Figs.  1-6 

1848.     Orthis  resupinata  Christy,  Letters  on  Geology,  pi.  3,  figs.  1-2. 
1858.     Orthis  sivallovi  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  597,  pi.  12,  figs. 

5a-b. 
1883.     Orthis  Swallovi  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.   (6)  36, 

figs.  23,  24. 
1892.     Orthis  Sivallovi  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  1,  pi.  6, 

figs.  23,  24. 
1894.     Orthis  sivallovi  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  63,  pi.  38,  fig.  5. 

Description. — Shell  large,  resupinate,  broader  than  long,  transversely 
subelliptical  in  outline,  often  slightly  emarginate  in  front,  the  hinge-line 
about  one-half  or  a  little  more  than  one-half  the  greatest  width,  the  car- 
dinal extremities  rounded.  The  dimensions  of  two  pedicle  valves  are: 
length  41  mm.  and  38.5  mm.,  width  51.7  mm.  and  49  mm.,  length  of  hinge- 
line  31  mm.  and  23  mm.,  height  of  cardinal  area  6  mm.  and  4  mm.,  convex- 
ity 9.2  mm.  and  7.5  mm.  The  dimensions  of  a  brachial  valve  are :  length 
39.6  mm.,  width  46.2  mm.,  convexity  14.3  mm. 

Pedicle  valve  nearly  flat  or  only  slightly  convex  over  the  greater  por- 
tion of  its  surface,  most  prominent  in  the  umbonal  region,  curving  some- 
what abruptly  to  the  cardinal  margin,  a  little  compressed  towards  the 
cardinal  extremities ;  the  median  portion  of  the  valve  usually  undifferen- 
tiated in  the  posterior  half  of  the  valve  and  becoming  slightly  depressed 
towards  the  front  in  a  broad,  shallow  and  undefined  sinus,  occasionally 
this  sinus  originates  in  the  umbonal  region,  and  sometimes  it  is  slightly 
more  depressed  at  either  side  towards  the  front  with  the  median  portion 
a  little  higher ;  beak  rather  small,  only  moderately  produced  beyond  the 
hinge-line  posteriorly ;  cardinal  area  rather  small,  concave,  with  the  curv- 
ature increasing  towards  the  beak,  broadly  triangular,  the  lateral  mar- 
gins well  defined  and  usually  slightly  concave  in  passing  from  the  beak 


IliS  .Mlssissil'l'lAN    BRACHIOPODA 

to  the  cardinal  extremities,  the  inferior,  flatter  portion  lying  nearly  at  a 
right  angle  to  the  plane  of  the  valve;  the  delthyrium  large,  broadly  tri- 
angular. Internally  the  cardinal  teeth  are  of  moderate  size,  and  are 
supported  by  short  dental  Lamellae  which  are  continued  anteriorly  as  low 
bounding  ridges  along  the  lateral  margins  of  the  muscular  scars;  the 
muscular  sears  rather  large,  sometimes  extending  anteriorly  beyond  the 
middle  of  the  valve,  sharply  defined  all  around  by  a  margin  which  is  ab- 
ruptly raised  from  the  inner  surface  of  the  valve,  subeordate  in  outline 
with  a  deep  and  acutely  angular  emarginat ion  in  front,  divided  longitud- 
inally from  the  base  of  the  emargination  to  the  beak  by  a  conspicuous, 
narrowly  rounded,  median  ridge  which  gradually  decreases  in  size  poste- 
riorly; each  lateral  lobe  marked  by  several  ill-defined,  more  or  less  incon- 
spicuous, radiating  ribs  which  are  strongest   anteriorly. 

Brachial  valve  much  more  convex  than  the  pedicle,  the  greatest  convex- 
ity posterior  to  the  middle,  the  umbo  prominent  and  extending  conspicu- 
ously beyond  the  cardinal  margin,  the  surface  curving  abruptly  to  the 
margin  on  all  sides  hut  most  abruptly  to  the  cardinal  margin,  somewhat 
compressed  towards  the  cardinal  extremities;  the  median  portion  of  the 
valve  distinctly  flattened  posteriorly,  the  flattened  region  becoming  im- 
pressed towards  the  front  in  a  shallow,  rounded  sinus  of  moderate  width; 
the  beak  pointed  and  rather  strongly  incurved;  the  cardinal  area  smaller 
than  that  of  the  opposite  valve,  its  lateral  margins  sharply  defined,  con- 
cave, curving  from  the  hinge-line  towards  the  beak  of  the  opposite  valve. 
The  internal  characters  of  the  valve  not  observed. 

Surface  of  both  valves  marked  by  fine,  regular,  radiating  costa?  which 
increase  by  bifurcation  and  intercalation,  about  two  or  three  occupying 
the  space  of  one  millimeter  at  the  front  of  a  full  grown  shell,  crossing 
the  costa?  are  more  or  less  irregular  concentric  lines  of  growth  which  are 
commonly  more  conspicuous  upon  the  brachial  valve,  and  are  usually 
somewhat  crowded  near  the  margin  of  full  grown  shells.  The  shell  sub- 
stance is  pierced  by  fine,  radiating  canals  or  tubules  which  apparently 
follow  the  direction  of  the  radiating  costae,  along  the  summit  of  which 
they  open  at  intervals. 

Remarks. — This  is  the  largest  of  our  species  of  Schizophoria,  and  is  a 
common  and  characteristic  fossil  of  the  Burlington  limestone.  It  may  be 
easily  recognized  by  its  large  size  and  the  very  slight  mesial  sinus  of  the 
pedicle  valve. 

Horizon. — Burlington  limestone. 


CAMAROPHORIA  169 

Family  PENTAMERID.E 

Genus  CAMAROPHORIA  King 

Description. — Shell  usually  small  or  below  medium  size,  rostrate,  subo- 
vate  to  subpentagonal  in  outline,  with  well-developed  median  sinus  in  the 
pedicle  valve  and  fold  in  the  brachial  valve,  both  valves  either  plicated 
or  with  the  plications  nearly  or  quite  obsolete.  In  the  pedicle  valve  the 
dental  lamella'  are  continued  anteriorly  into  a  well  developed  spondylium 
which  is  either  supported  by  a  median  septum  or  rests  directly  upon  the 
floor  of  the  valve  for  a  part  or  the  whole  of  its  length.  In  the  rostral 
portion  of  the  brachial  valve  the  hinge-plate  is  continuous  and  is  sup- 
ported by  a  strong  median  septum ;  between  the  hinge-plate  and  the  floor 
of  the  valve  the  median  septum  also  supports  a  concave  cruralium  which 
is  continued  far  beyond  the  hinge-plate,  becoming  broader  and  more 
highly  elevated  anteriorly ;  posteriorly  the  median  septum  passes  through 
the  cruralium  for  the  support  of  the  hinge-plate,  but  the  extension  of  the 
septum  above  the  concave  surface  of  the  cruralium  soon  disappears  be- 
yond the  anterior  margin  of  the  hinge-plate. 


*  b  CD 


©©©<© 

K 

Fig.  1. — A  series  of  eleven  cross-sections  (X  2%)  of  the  rostral  portion  of  Cam- 
arophoria  schlothcimi  (von  Buch),  the  genotype  of  Camarophoria,  from  the 
Permian  of  Possneck,  Germany,  showing  dental  lamella?  and  spondylium  of 
the  pedicle  valve,  and  the  median  septum,  cruralium  and  hinge-plate  of  the 
brachial  valve. 

Remarks. — Sometimes  the  genus  Camarophoria  has  been  so  interpreted 
as  to  include  a  number  of  rhynchonelloid  shells,  R.  subcuneata  and  R.  sub- 
trigona,  of  our  Mississippian  faunas  which  are  characterized  by  a  median 
septum  in  both  valves.  These  shells,  however,  do  not  possess  the  cruralium 
of  the  brachial  valve  and  are  therefore  excluded  from  the  family  Pentam- 
ericlce  and  are  included  in  the  present  report  in  the  Rhynchonellidce  under 
the  genus  Tetracamcra.  In  all  the  species  here  included  in  Camarophoria 
the  characteristic  internal  characters  of  the  shell  have  been  determined 
by  grinding  the  rostral  portion  of  the  shells.  For  comparison  similar 
sections  of  the  genotype,  C.  schlotheimi  (von  Buch),  have  been  made  and 
the  American  Mississippian  species  agree  in  all  essential  generic  charac- 
ters with  that  species  from  the  Permian  of  Germany. 


170  MISSISSIPPIAN   BBAC11IOPODA 

Camaropiioria  hamburgensis  Weller 
Plate  XXIII,  Pigs.  52-60 

1910.     Camaropiioria  hamburgensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21,  p. 
500,  fig.  2. 

Description. — Shell  below  medium  size,  subovate  in  outline,  the  length 
equal  to,  greater  or  less  than  the  width,  the  greatest  width  near  the  mid- 
length  of  the  shell.  The  postero-lateral  margins  nearly  straight,  and 
meeting  at  the  beat  in  an  angle,  the  lateral  and  anterior  margins  rounded. 
The  dimensions  of  a  small  but  nearly  perfect  specimen  are:  length  9.4 
nun.,  width  9.3  mm.,  thickness  5.5  mm.  The  dimensions  of  two  detached 
brachial  valves  are:  length  10.5  mm.  and  10  mm.,  width  13.5  mm.  and 
12.4  mm. 

Pedicle  valve  depressed  convex  in  the  posterior  half  and  towards  the 
antero-lateral  margins,  more  strongly  arched  from  the  beak  to  the  ante- 
rior margin,  along  the  postero-lateral  margins  the  edge  of  the  valve  is 
rather  abruptly  inflected  towards  the  opposite  valve  to  form  a  false  car- 
dinal area;  mesial  sinus  obsolete  in  the  posterior  half  of  the  valve,  orig- 
inating near  the  middle  and  continuing  to  the  anterior  margin  as  a  broad, 
shallow,  illdefined,  regularly  concave  depression,  whose  surface  curves 
towards  the  opposite  valve  anteriorly  and  is  a  little  produced  in  front  as 
a  broad  rounded  extension;  beak  rather  large,  a  little  incurved,  pierced 
by  a  subcircular  foramen;  delthyrium  broadly  triangular,  nearly  filled 
by  the  beak  of  the  opposite  valve,  its  apex  communicating  with  the  fora- 
men which  encroaches  upon  the  beak  of  the  valve ;  plications  depressed, 

?     r>     <r>     o      0>      <3^> 

<^    r^    r^    ^^ 


Fig.  2. — A  series  of  cross-sections  of  the  rostral  portion  of  the  shell  of  Cam- 
arophoria  hamburgensis  (X  21/£);  A  to  J  the  pedicle  valve;  K  to  T  the 
brachial   valve. 

mostly  simple,  rather  broad  and  rounded  on  top,  originating  at  or  near 
the  beak,  from  16  to  22  in  number,  from  5  to  7  of  which  occupy  the 
mesial  sinus,  those  towards  the  postero-lateral  margins  becoming  faint  or 
nearly  obsolete.     Internally  the  hinge-teeth  are  supported  by  dental  lam- 


CAMAROPHORIA  171 

ellae  -which  are  produced  anteriorly  more  than  one-third  the  length  of  the 
valve  as  a  spondylium-like  platform  which  rests  upon  the  floor  of  the 
valve,  not  being  raised  on  a  median  septum. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  the  surface  curving  downward  in  all  directions  from  the 
point  of  greatest  convexity  but  more  gently  to  the  anterior  margin  than 
in  other  directions ;  mesial  fold  obsolete  in  the  posterior  half  of  the  valve, 
only  moderately  elevated  in  front,  rounded  transversely  and  sometimes 
scarcely  differentiated  from  the  lateral  slopes ;  the  beak  broad,  strongly 
incurved  beneath  that  of  the  opposite  valve ;  the  plications  similar  in  form 
and  number  to  those  of  the  opposite  valve.  Internally  no  cardinal  pro- 
cess is  present,  the  hinge-plate  is  broad  and  not  divided  and  is  produced 
anteriorly  in  a  pair  of  crura,  at  the  apex  of  the  beak  it  is  supported  by  a 
median  septum  from  each  side  of  which,  at  a  position  about  midway  be- 
tween the  hinge-plate  and  the  floor  of  the  valve,  springs  a  lateral  process 
which  curves  slightly  away  from  the  floor  of  the  valve,  anteriorly  the 
hinge-plate  becomes  entirely  unsupported  by  the  median  septum  before 
the  articulation  of  the  hinge  is  past,  but  the  median  septum  itself  with 
its  transverse  processes  which  develop  into  a  broadly  V-shaped  platform 
extends  for  one-third  or  more  of  the  length  of  the  valve,  the  platform 
gradually  rising  higher  above  the  floor  of  the  valve  and  terminating  ab- 
ruptly with  the  septum  in  front,  posteriorly  the  median  septum  continues 
for  a  short  distance  towards  the  front  as  a  gradually  decreasing  longitud- 
inal ridge  in  the  bottom  of  the  V-shaped  platform. 

The  surface  of  both  valves,  in  addition  to  the  plications,  is  marked  by 
more  or  less  obscure  lines  of  growth. 

Remarks. — In  its  external  aspects  this  little  shell  resembles,  to  some 
extent,  some  of  the  Devonian  species  of  Pentamcrella,  but  its  internal 
characters  are  not  essentially  different  from  those  of  Camarophoria,  in 
which  genus  the  species  is  placed  without  any  hesitation.  The  spondy- 
lium-like platform  of  the  pedicle  valve  resting  upon  the  floor  of  the  valve, 
is  similar  to  the  condition  in  Cama/rophorella,  and  the  median  septum  of 
the  brachial  valve  with  its  transverse  processes  is  also  similar  to  that 
genus,  but  it  lacks  the  lateral  septa  which  in  that  genus  connect  the  outer 
margins  of  the  V-shaped  platform  with  the  floor  of  the  valve.  Camaro- 
phorella  has  been  shown  recently  to  be  a  spire  bearing  shell,1  but  there  is 
no  evidence  in  the  specimens  of  the  species  here  described  that  this  form 
possessed  any  brachidium  beyond  the  crura,  although  if  such  had  been 
present  it  would  have  been  destroyed  in  the  separated  valves  which  alone 
have  been  available  for  the  examination  of  the  internal  parts.  Externally, 
the  shell  is  distinctly  unlike  Camaropliorella  in  having  distinct  longitudinal 
plications. 

i  Hyde,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  34,  No.  3,  pp.  35-65     (1908). 


172  \iississiiri an    BRACHIOPODA 

Among  the  numerous  examples  of  the  species  which  have  heen  exam- 
ined, a  considerable  amounl  of  variation  is  exhibited  in  the  proportional 
lengtb  and  breadth  of  the  shells  and  in  the  strength  of  the  plications.  An 

occasional  example  is  round  upon  which  the  plications  are  essentially 
obsolete,  and  others  occur  on  which  they  are  obsolete  towards  the  beak, 
hut  in  all  other  respects,  both  external  and  internal,  so  far  as  they  can  be 
examined,  they  arc  identical  with  the  plicated  examples,  and  all  are  be- 
lieved to  belong  to  a  single  species. 

CaMABOPHOKLA  isisi.niata  (Rowley) 
Plate  XXIII,  Figs.  20-45 

1900,     Seminula  bisinuata  Rowley,  Am.  Geol.,  vol.  25,  p.  263,  pi.  5,  figs. 

21-24. 
1909.     Camarophoria  bisinuataf  Weller,    Bull.    Geol.    Soc.    Am.,  vol.  20, 

p.  301. 

Description. — Shell  .small,  subovate  to  subpentagonal  in  outline,  more 
or  less  subglobular  in  form,  the  length  greater  or  a  little  less  than  the 
width,  the  greatest  width  near  or  in  front  of  the  middle  of  the  shell.  The 
dimensions  of  two  examples,  met  a  types,  are:  length  of  pedicle  valve  9.2 
nun.  and  9  mm.,  length  of  brachial  valve  8.4  mm.  and  8  mm.,  greatest 
width  9.8  nun.  and  8.3  mm.,  thickness  6.1  mm.  and  6.3  mm. 

Pedicle  valve  arched  from  beak  to  front,  moderately  convex  in  the 
umboual  region,  the  curvature  of  the  surface  is  abrupt  and  somewhat 
inflected  from  the  umhonal  region  to  the  cardinal  margin,  and  more 
gentle  to  the  antero-lateral  margins;  mesial  sinus  obsolete  in  the  posterior 
half  of  the  valve,  rather  broad  and  shallow  anteriorly,  deepest  towards 
its  lateral  margins  with  a  low,  broad,  rounded  fold  in  the  middle,  pro- 
duced anteriorly  in  a  lingual  extension  whose  surface  lies  at  nearly  a  right 
angle  to  the  plane  of  the  valve ;  beak  small,  pointed  and  moderately  in- 
curved; plications  wanting  except  the  broad,  low,  median  fold  which  is 
usually  present  in  the  sinus.  Internally,  a  strong  median  septum,  about 
one-third  the  length  of  the  valve  extends  anteriorly  from  the  beak,  and 
supported  by  this  septum  is  a  distinct  spondylium. 

Brachial  valve  more  strongly  convex  than  the  pedicle,  becoming  gib- 
bous in  the  more  globular  examples,  the  greatest  depth  anterior  to  the 
middle  and  sometimes  close  to  the  anterior  margin,  the  surface  curving 
abruptly  from  the  middle  to  the  posterior,  lateral  and  antero-lateral 
margins ;  the  median  portion  of  the  anterior  half  of  the  valve  is  elevated 
in  a  mesial  fold  which  sometimes  gives  to  the  anterior  portion  of  the 
valve  a  trilobed  appearance,  along  its  median  line  the  fold  is  marked  by 
a  furrow  which  is  commonly  narrower  than  the  median  plication  of  the 
opposite  valve;  the  beak  is  pointed  and  incurved  beneath  that  of  the 
opposite  valve;  plications  absent  from  the  lateral  slopes  as  in  the  pedicle 


CAMAROPHORIA  173 

valve.  Internally  a  median  septum,  thinner  and  weaker  than  that  of  the 
pedicle  valve  extends  anteriorly  from  the  beak,  and  supports  both  the 
cruralium  and  the  binge-plate. 

The  surface  markings  of  the  shell  consist  of  rather  strong,  more  or 
less  regularly  arranged  concentric  lines  of  growth. 

*  <?  ®  ©  vj> 

E 

Fig.   3. — A   series  of  five   cross-sections    of    the    rostral   portion   of   the   shell   of 
Camarophoria  bisinuata  (X  21/£). 

Hi  marks. — This  species  was  originally  described  as  a  member  of  the 
genus  Seminula,  now  known  under  the  name  Composita,  and  in  its  gen- 
eral form  it  does  resemble  members  of  that  genus.  Some  examples,  even 
closely  resemble  small  specimens  of  C.  trinuclea,  and  under  certain  con- 
ditions of  preservation  it  might  be  difficult  to  separate  the  forms,  but 
internally  the  two  shells  are  fundamentally  different,  the  median  septum 
and  spondylium  being  entirely  wanting  in  Composita.  The  only  other 
species  of  Camarophoria  with  which  it  is  necessary  to  compare  this  one  is 
C.  explanata.  The  more  glolmlar  examples  of  C.  bisinuata  most  closely 
resemble  C.  explanata,  but  they  may  always  be  distinguished  by  the 
absence  of  any  plications  upon  the  lateral  slopes  of  the  valves. 

Horizon.— Fern  Glen  formation  and  lower  Burlington  limestone. 

Camarophoria  explanata   (McChesney) 
Plate  XXIII,  Figs.  46-51 

1860.     Rhynchonella  explanata  McChesney,  Desc.  New  Pal.  Foss.,  p.  50. 
1865.     Rhynchonella  explanata  McChesney,  Plates  111.  New  Spec.  Foss.,  pi. 

6.  figs.  7a-c. 
1868.     Rhynchonella  explanata  McChesney,  Trans.  Chicago  Acad.  Sci.,  vol. 

1,  p.  30,  pi.  6,  figs.  7a-c. 

1894.  Pugnax  explanatus  Hall  and  Clarke,  Int.  to  Study  of  Brack.,  pt.  2, 

pi.  44,  figs.  14-16. 

1895.  Pugnax  explanatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2.  pi.  60, 

figs.   43-45. 
1897.     Camarophoria  explanata  Schuchert,  Bull.  U.  S.  Geol.  Survey  No.  87. 

p.  162. 
1910.     Camarophoria  explanata  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21,  p. 

501,  fig.  3. 

Description. — Shell  small,  subglobular  in  form,  usually  a  little  wider 
than  long.  The  dimensions  of  the  type  specimen,  which  is  a  little  above 
the  average  size,  are :  length  8  mm.,  width  8.9  mm.,  thickness  7.5  mm. 
One  of  the  largest  examples  observed  has  a  length  of  10  mm.,  but  the 


174  MissiSSIlTIAN   BSACHIOPODA 

average  size  is  probably  ;i  little  less  than  thai  of  the  type  specimen  whose 
dimensions  ha\  e  been  given. 

Pedicle  valve  strongly  convex,  the  greatesl  convexity  nearest  the  mid- 
dle, the  surface  strongly  arched  from  beak  to  Eronl  and  also  transversely, 
the  slope  from  the  umbonal  region  most  abrupt  towards  the  cardinal  mar- 
gin, more  gentle  to  the  lateral  margins;  mesial  sinus  obsolete  in  the 
posterior  half  of  the  valve,  developed  as  a  broad,  shallow  depression 
anteriorly  and  somewhat  produced  in  front  in  a  lingual  extension  whose 
surface  is  nearly  at  right  angles  to  the  plane  of  the  valve;  beak  small, 
pointed,  incurved ;  plications  obsolete  posteriorly,  in  the  anterior  half 
of  the  shell  they  are  broad  and  rounded,  a  single  strong  one,  the  strongest 
one  on  the  valve  occupies  the  median  portion  of  the  sinus,  and  upon  each 
lateral  slope  of  the  valve  there  arc  two  or  three  weaker  ones.  Internally 
a  strong  median  septum  is  developed,  supporting  a  spondylium,  which  ex- 
tends  anteriorly  from  the  beak  for  one-third  or  one-half  the  length  of 
t  he  valve. 


<p    XD 


OQQ'0 


Fig.  4. — A  series  of  eleven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Camarophoria  cxplanata  (X  21/£),  showing  the  spondylium  and  the  manner  of 
development  of  the  cruralium  and  its  relation  to  the  hinge-plate. 

Brachial  valve  gibbous,  more  strongly  convex  than  the  pedicle,  the 
greatest  convexity  near  the  middle,  the  surface  curving  steeply  from  the 
middle  point  to  the  posterior,  lateral  and  antero-lateral  margins  and  more 
gently  to  the  anterior  margin;  mesial  fold  obsolete  in  the  posterior  half 
of  the  valve  and  only  moderately  elevated  in  front,  it  is  divided  into  two 
rounded  folds  by  a  median  rounded  furrow  which  originates  near  the 
middle  of  the  valve  to  correspond  with  the  median  plication  of  the  sinus 
of  the  opposite  valve ;  the  beak  is  strongly  incurved  beneath  that  of  the 
opposite  valve ;  the  plications  are  similar  to  those  of  the  opposite  valve ; 
besides  the  two  plications  of  the  fold,  already  mentioned,  there  are  two 
or  three  upon  each  lateral  slope,  none  of  which  originate  posterior  to  the 
middle  of  the  valve  and  the  smaller  ones  even  nearer  to  the  margin.  In- 
ternally this  valve  has  a  median  septum  extending  forward  from  the  beak, 
but  it  is  thinner  and  more  feebly  developed  than  that  of  the  pedicle  valve ; 
it  supports  the  cruralium  and  the  hinge-plate. 


CAMAROTCECHIA  175 

The  surface  is  marked  only  by  concentric  lines  of  growth  which  are 
irregularly  developed,  frequently  being  obscure  or  wholly  obsolete. 

Remarks.— In  its  general  form  this  species  resembles  members  of  the 
rhynchonelloid  genus  Pugnax,  but  it  differs  fundamentally  from  members 
of  that  genus  in  having  a  distinct  spondylium  in  the  pedicle  valve  sup- 
ported by  a  median  septum.  This  septum,  and  also  that  of  the  opposite 
valve,  is  almost  always  clearly  recognizable,  except  in  silicifled  specimens, 
as  a  dark  line  extending  anteriorly  from  the  beak.  Hall  and  Clarke  re- 
ferred the  species  to  Pugnax  doubtless  because  the  specimen  which  they 
studied  and  illustrated  was  a  very  perfect  sulphur  cast  of  McChesney's 
type  specimen,  but  upon  which  there  was,  of  course,  no  color  differentia- 
tion which  would  lead  to  the  recognition  of  a  septum. 

The  species  is  very  distinct  from  all  other  members  of  the  genus  in  our 
American  Mississippian  faunas,  and  can  be  confused  with  none  of  them. 
It  occurs  abundantly  in  some  of  the  Chester  faunas  where  it  is  a  highly 
characteristic  species. 

Horizon. — Chester  group. 

Order  TELOTREMATA 

Family  RHYNCHONELLID^E 

Genus  CAMAROTCECHIA  Hall  and  Clarke 

Description.  —  Shell  rhynchonelliform,  small  or  below  medium  size, 
subovate,  subpentangular  or  subtriangular  in  outline.  The  mesial  fold 
and  sinus  well  developed,  the  surface  of  both  valves  marked  by  angular 
or  subangular  plications  which  extend  to  the  beak,  the  plications  not 
medially  grooved  in  front.  In  the  pedicle  valve  the  hinge-teeth  are 
rather  small  and  are  supported  by  slender,  vertical,  dental  lamella}.  In 
the  brachial  valve  a  well-defined  median  septum  is  present  in  the  rostral 
portion  of  the  valve  which  is  divided  internally  to  form  a  V-shaped  crural 
cavity,  the  hinge-plate  is  divided,  the  inner  margin  of  each  lateral  portion 
being  supported  by  one  of  the  lateral  walls  of  the  crural  cavity ;  no  car- 
dinal process  is  present  and  the  crura  are  formed  by  the  anterior  extension 
of  the  inner  margins  of  the  two  divisions  of  the  hinge-plate. 

Remarks.— The  essential  generic  characters  of  Camarotcechia  are  found 
in  a  combination  of  the  internal  and  external  features  of  the  shell.  The 
median  septum  of  the  brachial  valve  supporting  the  V-shaped  crural 
cavity  and  the  divided  hinge-plate  are  identical  in  all  essential  respects 
with  the  rostral  characters  of  Wilsonia,  Liorhynchus,  Paryphorhynclms 
and  Pugnoides,  the  five  genera  being  differentiated  one  from  another 
by  constant  external  characters.  In  Wilsonia  the  shell  is  subcubical  in 
form  with  the  plications  flattened  anteriorly  and  longitudinally  grooved, 
especially  in  the  fold  and  sinus.     Liorhynchus  is  a  larger  shell  with  the 


176 


MISSISSIPPI  AN     KKA(']]K>1'(II>A 


plications  usually  nearly  obsolete  upon  the  lateral  slopes  of  the  valves. 
Paryphorhynchus  also  is  a  much  Larger  shell  with  the  entire  external 
surface  of  1  lie  valves  marked  by  line  radiating  striae  in  addition  to  the 
plications,  and  Pugnoides  has  the  plications  becoming  obsolete  towards 
the  beak. 

Camakotckciiia  ciioi  tkai  knsis  Welter 
Plate  XXIV,  Figs.  34-40 

1910.     Camarotachia  choutemensis  Weller,  Bull.  Geol.  Soe.  Am.,  vol.  21, 
p.  510,  fig.  10. 

Description. — Shell  small  and  thick,  triangularly  subovate  in  outline, 
wider  than   long,  the  greatest   width   near  or  in    front  of  the  middle,  the 

postero-latcral    margins    ting    at    the    beak    in    an   obtuse   angle,    the 

lateral  margins  rounded,  the  anterior  margin  gently  convex.  The  dimen- 
sions of  two  nearly  perfect  specimens  are:  length  11  mm.  and  9.3  mm., 
width  11.5  mm.  and  10  mm.,  thickness  10  mm.  and  8  mm.,  width  of  sinus  in 
front   7  mm.  and  5.6  mm. 

Pedicle  valve  shallow,  narrowly  convex  on  the  umbo,  the  surface  sloping 
from  the  umbo  to  the  cardinal  margin,  at  first  with  an  abrupt  convex 
curvature,  becoming  gently  concave  as  it  approaches  the  margin,  towards 
the  antero-latcral  margins  the  surface  is  gently  convex  and  from  the 
beal<  to  the  front  along  the  median  line  it  is  strongly  and  nearly  regularly 
arched;  the  mesial  sinus  originates  near  the  mid-length  of  the  shell,  it  is 
abruptly  depressed,  its  surface  is  nearly  straight  or  slightly  convex 
transversely  across  the  bottom  and  is  strongly  curved  towards  the  oppo- 
site valve  longitudinally,  anteriorly  it  is  produced  into  a  broad,  elongate, 
lingual  extension  which  lies  in  nearly  a  right  angle  to  the  plane  of  the 
valve,  its  greatest  width  is  equal  to  about  one-half  the  total  width  of  the 
valve ;  the  beak  is  small  and  moderately  incurved ;  the  delthyrium  is 
nearly  filled  by  the  beak  of  the  other  valve,  the  deltidial  plates  and 
foramen  are  obscure  and  have  not  been  observed  in  the  specimens 
studied;  the  plications  are  sharply  angular  and  originate  at  the  beak, 
three  or  four  occupy  the  bottom  of  the  sinus,  these  being  a  little  less 
angular  than  those  upon  the  lateral  slopes,  each  lateral  slope  bears  from 
six  to  eight  plications  which  become  successively  fainter  towards  the 

98888866 

0  H 

Fig.  5. — A  series  of  eight  cross-sections  of  the  rostral  portion  of  the  shell  of 
Camarotwchia  chouteauensis  (X  2%),  showing  the  characters  of  the  median 
septum,  crural  cavity,  hinge-plate,  and  crura  of  the  brachial  valve,  and  the 
dental  lamellae  of  the  pedicle  valve. 


CAMAEOTCECHIA  177 

cardinal  margin,  the  hist  two  or  sometimes  three  being  almost  obsolete. 
Internally,  the  hinge-teeth  are  supported  by  short,  dental  lamellae  which 
scarcely  extend  beyond  the  articulation  of  the  hinge. 

Brachial  valve  gibbous,  the  greatest  depth  at  or  near  the  anterior 
margin,  the  surface  sloping  from  the  anterior  margin  to  the  beak  along 
the  median  line  with  a  convex  curvature  which  is  a  little  flattened  in 
the  middle  portion,  the  umbonal  region  flattened  transversely  with  a  dis- 
tinct longitudinal  median  depression  which  continues  anteriorly  for  about 
one-fourth  the  length  of  the  valve ;  the  median  fold  not  differentiated  in 
the  posterior  half  of  the  valve,  flattened  or  gently  convex  on  top  and 
only  moderately  elevated  above  the  lateral  slopes  anteriorly;  lateral  slopes 
strongly  convex  longitudinally  and  curving  abruptly  to  the  margin  of 
the  shell  laterally  ;  the  beak  strongly  incurved  beneath  that  of  the  opposite 
valve;  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve,  those  of  the  lateral  slopes  strongly  arched  longitudinally.  In- 
ternally no  cardinal  process  is  present,  the  hinge-plate  is  divided  and  is 
supported  towards  the  beak  by  a  divided  median  septum  which  forms 
a  crural  cavity,  the  support  of  the  hinge-plate  by  the  divided  median 
septum  is  discontinued  posterior  to  the  articulation  of  the  hinge,  but  the 
free  septum  continues  for  about  one-third  the  length  of  the  valve,  gradually 
becoming  lower  until  it  disappears. 

A  few  obscure  concentric  lines  of  growth  are  sometimes  present,  but 
the  shell  is  usually  smooth  aside  from  the  plications. 

Remarks.— This  little  shell  is  a  common  form  in  the  fauna  of  the 
Chouteau  limestone  and  may  be  easily  recognized  by  its  size  and  angular 
plications.  It  differs  from  L'hynchopora?  cooperensis  of  the  same  fauna 
in  its  smaller  size,  relatively  narrower  shell  and  smaller  number  of  plica- 
tions on  the  fold  and  sinus. 

Horizon.  —  Chouteau    limestone. 

Camakotcechia  klegantula  Rowley 
Plate  XXIV,  Figs.  1-8 

1900.  Camarotaehia  elegantula  Rowley,  Am.  Geol.,  vol.  25,  p.  264,  pi.  5, 
figs.  41-47. 
Description.— Shell  small,  broader  than  long,  the  postero-lateral  margins 
nearly  straight  or  slightly  concave  and  meeting  at  the  beak  in  an  angle 
of  from  90  to  110  degrees,  the  antero-lateral  and  anterior  margins  rounded. 
The  dimensions  of  three  nearly  complete  specimens  are:  length  of  pedicle 
valve  7.5  mm.,  9.5  mm.,  and  8.5  mm.;  length  of  brachial  valve  7  mm.,  8.5 
mm.,  and  7.6  mm.;  greatest  width  8.3  mm.,  11.6  mm.  and  9.4  mm.;  thick- 
ness 5.1  mm.,  6.7  mm.,  and  6  mm.;  width  of  sinus  in  front  6  mm.,  8  mm., 
and  5.9  mm. 


178  MISSISSIPPIAN  BRAC1II0P0DA 

Pedicle  valve  convex  in  the  umhonal  region,  the  surface  curving  ab- 
rupt I v  to  the  posterolateral  margins  and  sloping  with  a  gently  convex 
curvature  to  the  antero-lateral  margins  or  sometimes  becoming  a  little 
concave  as  it  approaches  the  margin,  from  beak  to  front  along  the  median 
line  the  curvature  of  the  surface  is  nearly  a  semicircle:  mesial  sinus  orig- 
inating near  the  middle  of  the  valve,  of  only  moderate  depth,  nearly  flat, 
or  sometimes  gently  convex  across  the  bottom  transversely,  produced  an- 
teriorly in  a  rather  broadly  rounded  or  truncate  lingual  extension,  the 
beak  sharply  pointed  and  incurved,  obscuring'  the  delthryiuin.  Surface 
marked  by  sharply  angular,  simple  plical  ions  which  originate  at  the  beak, 
there  being  from  four  to  six  on  the  bottom  of  the  sinus  and  about  five  on 
each  lateral  slope  of  the  valve,  the  largest  plications  of  the  valve  are  those 
bounding  the  sinus,  those  of  the  lateral  slopes  growing  rapidly  smaller, 
the  last  one  towards  the  cardinal  extremities  being  very  faint  or  almost 
obsolete.  Internally  the  dental  lamellae  are  of  moderate  length  and  but 
slightly  diverging  anterior. 

Brachial  valve  move  convex  than  the  pedicle,  the  greatest  depth  near 
the  anterior  margin,  posteriorly  from  the  point  of  greatest  convexity  the 
surface  slopes  with  a  very  gently  convex  curvature  which  becomes 
rapidly  more  convex  in  the  posterior  half  of  the  distance,  anteriorly  from 
the  same  point  the  curvature  is  short  and  abrupt,  laterally  the  surface 
curves  rather  abruptly  to  the  margins  from  the  median  portion  of  the 
valve  which  is  gently  convex  transversely;  mesial  fold  originating  near 
the  middle  of  the  valve,  not  conspicuously  differentiated  from  the  gen- 
eral convexity  except  towards  the  anterior  margin;  beak  pointed  and 
strongly  incurved  beneath  that  of  the  opposite  valve.  Surface  marked 
by  simple  plications  similar  to  those  of  the  opposite  valve  but  a  little  less 
angular.  Internally  a  median  septum  reaches  anteriorly  from  the  beak 
for  about  one-third  the  length  of  the  valve,  this  septum  divides  internally 
in  the  manner  characteristic  of  the  genus,  forming  a  crural  cavity  between 
the  margins  of  the  divided  hinge-plate. 

Minute  surface  markings  obscure  upon  the  specimen  studied. 

Remarks. — The  above  description  of  this  species  has  been  prepared  from 
specimens  collected  by  Professor  Rowley  from  the  original  locality  and 
identified  by  him  as  being  members  of  his  species,  specimens  which  are, 
therefore,  metatypes.  The  species  is  characterized  by  a  width  greater 
than  its  length,  its  angular  plications,  and  the  variable  number  of  plica- 
tions in  the  sinus.  It  differs  from  C.  tuta,  which  is  associated  with  it  at  the 
type  locality,  in  its  greater  proportional  width,  its  more  angular  plications, 
and  the  greater  depth  of  the  sinus  in  front. 

Horizon. — Lower  Burlington  limestone  (white  chert.) 


CAMAROTCECIIIA  179 

Camarotcechia  tuta  (Miller) 
Plate  XXIV,  Figs.  9-28 

1881.     Rhynchonella  tuta  Miller,  Jour.  Cinn.  Soc.  Nat.  Hist.,  vol.  4,  p.  315, 
pi.  7,  figs.  11-llb. 

Description.  —  Shell  small,  length  and  width  subequal  or  somewhat 
longer  than  wide,  subovate  in  outline,  the  greatest  width  near  or  a  little 
anterior  to  the  mid-length,  the  posterolateral  margins  nearly  straight, 
sometimes  a  little  concave  or  a  little  convex,  the  antero-lateral  and  an- 
terior margins  rounded  or  the  anterior  margin  somewhat  truncated.  The 
dimensions  of  a  nearly  complete  specimen  from  the  type  locality  are : 
length  of  pedicle  valve  6.4  mm.,  length  of  brachial  valve  5.7  mm.,  greatest 
width  6.3  mm.,  thickness  4.5  mm.,  width  of  sinus  in  front  4.1  mm.  The 
dimensions  of  a  specimen  from  the  Burlington  white  chert  at  Louisiana, 
Missouri,  are :  length  of  pedicle  valve  7.3  mm.,  length  of  brachial  valve 
6.7  mm.,  greatest  width  7.5  mm.,  thickness  5  mm.,  width  of  sinus  in  front 
4.3  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  the  surface  curving  ab- 
ruptly to  the  postero-lateral  margins,  gently  convex  from  the  umbonal 
region  to  the  antero-lateral  margins  and  arched  in  a  subsemicircular  curve 
along  the  mesial  line  from  beak  to  front,  with  the  posterior  curvature 
a  little  more  abrupt  than  the  anterior:  mesial  sinus  originating  near  the 
mid-length  of  the  valve,  nearly  flat  iu  the  bottom  transversely,  produced 
anteriorly  in  a  rather  broadly  rounded  or  subi'ectangular  lingual  ex- 
tension ;  beak  small,  pointed,  strongly  incurved,  coming  nearly  in  con- 
tact with  the  umbo  of  the  opposite  valve,  the  delthyrium  and  deltidial 
plates  obscured  by  the  incurvature  of  the  beak;  plications  simple,  originat- 
ing at  the  beak,  rounded,  becoming  subangular  towards  the  front,  four 
usually  if  not  always  occupying  the  sinus,  with  about  five  upon  each 
lateral  slope  which  become  successively  smaller  towards  the  cardinal  ex- 
tremities ;  concentric  markings  obscure  or  obsolete.  Internally  the  dental 
plates  are  delicate  and  of  moderate  length,  and  are  not  widely  divergent 
anteriorly  from  the  beak. 

Brachial  valve  more  strongly  convex  than  the  pedicle,  the  greatest 
convexity  anterior  to  the  middle,  sometimes  near  the  front  margin,  the 
surface  arched  from  the  beak  to  the  front  along  the  median  line,  usually 
with  the  curvature  more  pronounced  posteriorly,  the  curvature  more 
convex  to  the  antero-lateral  margins,  becoming  abrupt  to  the  postero- 
lateral margins;  mesial  fold  originating  near  the  mid-length  of  the  valve, 
not  strongly  differentiated  from  the  general  curvature  of  the  valve 
except  close  to  the  anterior  margin,  in  the  umbonal  region  a  shallow, 
longitudinal,  broadly  subangular,  mesial  depression  is  present,  which  is 
deepest  at  the  beak  and  becomes  obsolete  before   the  point  of  origin 


180  MISSISSII'I'IAN    BRACHIOPODA 

of  the  mesial  fold;  the  beak  strongly  incurved  beneath  that  of  the  oppo- 
site valve;  the  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve  and  alternate  with  them,  the  concentric  markings  also 
similar  to  those  of  the  opposite  valve. 

I,'<  marks.  This  is  a  small  species  which  was  originally  described  from 
New  .Mexico  and  the  ahove  description  lias  been  drawn  up  from  speci- 
mens collected  at  the  type  locality.  Examples  of  the  same  species  seem 
to  he  present  in  the  Chouteau  limestone  of  Missouri  and  Illinois,  at  least 
no  characters  have  been  detected  which  seem  to  he  of  sufficient  import- 
ance to  differentiate  the  two  forms,  although  the  Chouteau  limestone 
examples  seem  to  he  somewhat  more  rotund  and  have  slightly  less  angular 
plications  anteriorly  in  the  sinus. 

Horizon. — Chouteau  limestone  and  lower  Burlington  limestone. 

Camarotcechia  sublogosa  d.  sp. 
Plate  XXIV,  Figs.  29-)!:! 

Description. — Shell  small,  subglobose  in  form,  the  outline  subovate,  the 
length  greater  than  the  width,  the  greatest  width  near  the  mid-length  of 
the  shell.  The  dimensions  of  a  nearly  perfect  internal  cast  are:  length 
of  pedicle  valve  12.5  mm.,  length  of  brachial  valve  10.7  mm.,  greatest 
width  10.8  mm.,  thickness  9  mm.,  width  of  sinus  in  front  5.9  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  near  the  middle, 
the  surface  curving  abruptly  to  the  postero-lateral  margins,  less  abruptly 
to  the  antero-lateral  and  more  gently  to  the  anterior  margin ;  mesial  sinus 
originating  near  or  a  little  back  of  the  middle  of  the  valve,  only  slightly 
depressed  below  the  general  surface,  nearly  flat  transversely  across  the 
bottom,  produced  anteriorly  in  a  rather  short  and  broad  mesial  extension ; 
beak  rather  prominent  in  the  internal  casts  and  only  moderately  in- 
curved ;  plications  simple,  subangular,  probably  extending  to  the  beak 
upon  the  external  surface  but  becoming  faint  and  obsolete  towards  the 
beak  on  the  internal  cast,  three  are  present  in  the  sinus  and  seven  or  eight 
upon  each  lateral  slope,  the  last  two  or  three  towards  the  cardinal  ex- 
tremities becoming  faint  and  at  last  nearly  obsolete ;  rather  crowded,  fine, 
concentric  lines  of  growth  are  present  upon  the  internal  cast  over  at  least 
the  anterior  half  of  the  valve,  with  an  occasional  stronger  one,  and  upon 
the  external  surface  these  markings  were  doubtless  strongly  developed 
over  the  entire  surface  of  the  valve.  Internally  the  dental  plates  are 
rather  strong  and  of  moderate  length  and  between  them  is  a  well  defined 
muscle  scar  which  extends  anteriorly  for  about  one-third  the  length  of 
the  valve. 

Brachial  valve  subcircular  in  outline,  but  little  more  convex  than  the 
pedicle,  its  greatest  convexity  near  the  middle,    the   surface  describing 


CAMAROTCECIIIA  181 

nearly  a  subsemicireular  curve  along  the  median  line  from  the  beak  to  the 
front,  and  curving  rather  abruptly  to  the  lateral  margins ;  mesial  fold 
originating  near  the  middle  of  the  valve,  only  a  little  elevated  above  the 
general  surface  towards  the  front;  the  beak  pointed  and  incurved  be- 
neath that  of  the  opposite  valve ;  the  plications  and  concentric  markings 
similar  in  form  and  number  to  those  of  the  opposite  valve.  Internally  a 
strong  median  septum  extends  anteriorly  from  the  beak  nearly  or  quite 
to  the  center  of  the  valve,  in  the  rostral  portion  of  the  valve  this  septum 
divides  internally  forming  a  short  crural  cavity  between  the  two  lateral 
portions  of  the  divided  hinge-platt. 

Remarks.- — This  species  has  only  been  observed  in  the  form  of  internal 
c;ists  from  the  residual  Burlington  chert  of  Knox  County,  Missouri,  it  may 
be  easily  recognized  by  its  subglobose  form,  its  rather  coarse  plications 
and  its  shallow  mesial  sinus  and  low  fold. 

Formation.— Burlington  limestone  (residual  chert). 

Camarotcechia  mutata  (Hall) 

Plate  XXIV,  Figs.  41-60 

1856.     Bhynchonella  mutata  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  10. 
1858.     Bhynchonella  mutata  Hall.  Geol.  Iowa,  vol.  1,  pt.  2,  p.  658,  pi.  23, 

figs.  2a-b. 
1882.     Bhynchonella  mutata  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

p.  52,  pi.  6,  figs.  43-45. 
1883     Bhynchonella  mutata  Hall.  12th  Rep.  Geol.  Surv.  Ind.,  p.  332,  pi. 

29,  figs.  43-45. 

1894.  Bhynchonella  mutata  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  103. 

1895.  Pugnax  via  fat  us  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  60, 

figs.  18-22. 
1906.     Pugnax  mutata  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1306,  pi. 
22,  figs.  43-45. 

Description. — Shell  subovate  or  subtriangular  in  outline,  usually  wider 
than  long,  the  greatest  width  in  front  of  the  mid-length  of  the  shell,  the 
postero-lateral  margins  straight  or  nearly  straight,  meeting  at  the  beak 
in  an  angle  of  from  80  to  100  degrees,  the  anterior  margin  truncate,  the 
antero-lateral  margins  more  or  less  sharply  rounded.  The  dimensions  of 
two  individuals  are :  length  9.7  mm.  and  8.9  mm.,  width  10.6  mm  and  9.1 
mm.,  thickness  7  mm.  and  5.5  mm.,  width  of  sinus  in  front  7.8  mm.  and 
5.8  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  usually  somewhat  flattened 
in  the  middle  and  towards  the  antero-lateral  margins,  the  surface  curves 
rather  abruptly  to  the  postero-lateral  margins,  gently  to  the  antero-lateral 
margins  and  is  arched  from  the  beak  to  the  front ;  along  the  postero-lateral 
margins  towards  the  beak,  the  edge  of  the  valve  is  inflected  to  form  a 
more  or  less  indistinct  pseudo-cardinal  area,  this  area  becoming  less  dis- 
tinct in  the  older  shells;  mesial  sinus  obsolete  in  the  posterior  half  of  the 


ih2  M  ississil'l'lAN    BRACHIOPODA 

shell,  anteriorly  il  is  broad  and  shallow,  its  surface  is  curved  towards  the 
Opposite  valve,  and  its  anterior  margin  is  produced  more  or  less  conspic- 
uously beyond  the  lateral  margins;  the  beak  is  pointed,  only  slightly  in- 
curved and  is  produced  posteriorly  beyond  that  of  the  opposite  valve; 
the  delthyriuni  is  broadly  triangular  and  is  partially  closed  by  deltidial 
platea,  with  a  suhcircular  foramen  at  the  apex;  plications  simple,  suban- 
gular,  becoming  faint  or  obsolete  close  to  the  beak,  fourteen  to  twenty  in 
number,  from  three  to  six  of  which  occupy  the  median  sinus,  the  first  two 
or  three  on  each  side  nearest  the  postero-lateral  margins  are  very  faint. 
Internally  Hie  teeth  are  supported  by  short  dental  lamellse  which  do  not 
continue  anteriorly  beyond  the  articulation  of  the  hinge. 

Brachial  valve  more  strongly  convex  than  the  pedicle,  the  greatest 
depth  anterior  to  the  middle  and  in  adult  shells  near  the  anterior  margin; 
from  the  point  of  greatest  convexity  the  surface  curves  more  or  less  ab- 
ruptly to  the  anterior  margin  and  more  gently  to  the  posterior  extremity, 
laterally  the  surface  curves  somewhat  abruptly  to  the  postero-lateral 
margins,  but  the  median  portion  of  the  valve  is  somewhat  flattened  trans- 
versely ;  mesial  fold  scarcely  defined  except  upon  the  more  or  less  abrupt 
anterior  slope  of  the  valve  and  even  there  it  is  scarcely  differentiated 
from  the  remainder  of  the  valve;  the  beak  strongly  incurved  beneath 
that  of  the  opposite  valve;  plications  similar  in  form  and  number  to  those 
of  the  opposite  valve.  Internally  no  cardinal  process  is  present,  the 
hinge-plate  is  longitudinally  divided  to  the  apex  of  the  beak  and  in  the 
extreme  posterior  portion  of  the  valve  it  is  supported  by  a  median  septum 
which  is  divided  above,  each  division  of  the  hinge-plate  being  supported 
by  one  limb ;  the  divided  median  septum  with  its  crural  cavity  be- 
tween the  divisions  of  the  hinge-plate  is  extremely  short  and  disappears 
posterior  to  the  dental  sockets,  anteriorly  the  median  septum  is  free  and 
is  reduced  rapidly  in  height  to  a  slight  ridge  along  the  bottom  of  the 
valve  which  sometimes  continues  for  one-half  the  length  of  the  valve;  the 
divided  hinge-plate  becomes  nearly  horizontal  anteriorly  where  its  anterior 
extremity  is  produced  into  the  crura. 

The  surface  of  both  valves,  aside  from  the  plications,  is  nearly  or  quite 
smooth  save  for  a  few  rather  inconspicuous  lines  of  growth  near  the  an- 
terior margin  of  adult  shells. 

Remarks. — This  species  is  one  of  the  abundant  forms  in  the  fauna  of  the 
Salem  limestone.  It  was  originally  described  from  near  Alton,  Illinois, 
and  in  some  of  the  Salem  limestone  localities  in  the  bluffs  above  that  city, 
it  is  particularly  abundant.  It  is  a  variable  shell,  the  variations  being 
exhibited  in  the  dimensions,  convexity  of  the  valves,  fold  and  sinus,  and 
number  of  plications.  It  differs  from  C.  grosvenori,  which  occurs  com- 
monly in  the  same  fauna  in  Indiana,  in  its  larger  size,  stronger  and  more 
angular  plications  and  less  globular  form. 


CAMAROTCECHIA  183 

The  species  has  sometimes  been  referred  to  the  genus  Pugnax,  but  such 
reference  is  incorrect.  Besides  being  quite  different  from  typical  mem- 
bers of  that  genus  in  external  characters  it  possesses  a  crural  cavity  sup- 
ported by  a  median  septum  at  the  base  of  the  divided  hinge-plate  a  char- 
acter which  is  typical  of  the  genus  Camarotcechia. 

Horizon.^- Salem  limestone. 

Camarotcechia  grosvenori   (Hall) 
Plate  XXIV,  Figs.  61-72 

1856.     Rhynchonella  Grosvenori  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  10. 

1882.  Ehijnehonclla  Grosvenori  Whitfield,  Bull.  Am.  Mus.  Nat.  Mist.,  vol. 

1,  p.  53,  pi.  6,  figs.  31-34. 

1883.  Rhynchonella  grosvenori   Hal],    12th   Ann.   Rep.    Geol.    Surv.    Ind., 

p.  331,  pi.  29,  figs.  31-34. 
1895.     Pugnax  Grosvenori  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  HO. 

figs.  13-17. 
1901.     Wilsonia   Grosvenori   Whitfield   and   Hovey,   Bull.   Am.   Mus.   Nat. 

Hist.,  vol.  11,  p.  388. 
1906.     Pugnax  grosvenori  Beede   30th  Ann  Rep   Geol.  Surv.  Ind.,  p.  1305. 

pi.  22,  figs.  31-34. 
1910.     Wilsonia  grosvenori  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21.  p.  510, 

fig.  11.  * 
Description. — Shell  small,  subglobular  in  form,  the  width  equal  to, 
greater  than  or  less  than  the  length,  the  greatest  width  near  or  in  front 
of  the  mid-length,  the  postero-lateral  margins  gently  convex  or  nearly 
straight,  meeting  at  the  beak  in  an  angle  of  90  degrees  or  less,  the  ante- 
rior and  antero-lateral  margins  more  or  less  regularly  rounded.  The  di- 
mensions of  a  large  individual  are:  length  7  mm.,  width  6.5  mm.,  thick- 
ness 5.5  mm.,  width  of  sinus  in  front  4.5  mm. 

Pedicle  valve  more  or  less  regularly  convex  throughout,  the  surface 
curving  somewhat  more  abruptly  to  the  postero-lateral  margins,  arched 
from  beak  to  front ;  for  a  short  distance  on  each  side  of  the  beak  the  edge 
of  the  valve  along  the  postero-lateral  margins  is  somewhat  abruptly  and 
sharply  inflected  to  form  a  small  pseudo-cardinal  area ;  mesial  sinus  obso- 
lete in  the  posterior  half  of  the  shell  and  sometimes  obsolete  throughout, 
usually  it  is  broad  and  slightly  depressed  anteriorly  and  is  produced  an- 
teriorly in  a  broad  lingual  extension  which  is  curved  towards  the  opposite 
valve  to  such  an  extent  that  its  surface  lies  at  nearly  a  right  angle  to  the 
general  plane  of  the  valve  in  front ;  beak  pointed,  a  little  incurved  and 
projecting  posteriorly  beyond  the  hinge-line ;  delthyrium  broadly  trian- 
gular, partially  closed  by  deltidial  plates,  with  a  subcircular  foramen  at 
the  apex  which  encroaches  to  some  extent  upon  the  beak  of  the  valve ; 
plications  simple,  rounded,  from  18  to  22  in  number,  two  or  three  of  which 
on  each  side  near  the  cardinal  margins  are  very  small,  from  three  to  six 
are  included  in  the  mesial  sinus,  four  or  five  being  the  more  usual  num- 


L84  MISSISSIPPIAN    BRACH10P0DA 

hers.  Internally  the  teeth  are  supported  by  a  pair  of  short  dental  plates 
winch  become  Obsolete  anterior  to  the  articulation  of  the  hinge. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  depth  anterior 
to  the  middle  and  sometimes  close  to  the  anterior  margin,  from  the  point 
of  greatest  convexity  the  surface  curves  more  or  less  gently  to  the  poste- 
rior extremity,  transversely  the  surface  is  rather  regularly  convex  but  it 
curves  a  little  more  abruptly  as  it  approaches  the  lateral  margins;  mesial 
fold  obsolete  posteriorly  and  scarcely  or  not  at  all  differentiated  on  the 
more  or  less  abrupt  anterior  slope  of  the  valve;  the  beak  incurved  be- 
neath that  of  the  opposite  valve ;  plications  similar  in  character  and  num- 
ber to  those  of  the  opposite  valve.  Internally  the  hinge-plate  is  divided 
to  its  base  and  the  cardinal  process  is  lacking,  at  the  extreme  posterior 
apex  of  the  valve  a  median  septum  is  present,  winch  is  divided  above  to 
support  the  two  limbs  of  the  hinge-plate  forming  a  crural  cavity,  this 

?     ?     9     9     Q 

Fig.  6. — A  series  of  five  cross-sections  of  the  rostral  portion  of  the  shell  of 
Camarotccchia  grosvenori  (X  2%),  showing  the  dental  lamella?  in  the  pedicle 
valve  and  the  short  median  septum  and  small  crural  cavity  in  the  brachial 
valve. 

cavity  disappears  posterior  to  the  articulation  of  the  hinge  and  the  median 
septum  is  rapidly  reduced  in  height,  although  it  frequently  persists  as  a 
slight  median  ridge  to  the  middle  of  the  valve. 

Aside  from  the  plications  the  surface  of  both  valves  is  nearly  or  quite 
smooth  except  in  fully  grown  shells  which  have  a  few,  distinct,  parallel 
lines  of  growth  close  to  the  margin. 

lu  marls.— This  species  occurs  commonly  in  the  Salem  limestone  fauna 
in  Indiana,  but  in  the  Illinois  localities  it  is  a  rare  shell.  It  resembles 
somewhat  closely  some  of  the  variations  of  C.  mutata,  and  in  most  large 
collections  of  the  latter  species  a  few  individuals  may  usually  be  selected 
wdiich  by  themselves  might  be  referred  to  C.  grosvenori.  Typical  repre- 
sentatives of  the  two  species,  however,  are  quite  distinct.  C.  grosvenori 
is  a  smaller  species,  much  more  globular  in  form,  with  a  much  less  well 
developed  sinus  in  the  pedicle  valve,  and  with  finer  and  less  angular  pli- 
cations. Many  and  perhaps  a  majority  of  examples  of  G.  grosvenori  are 
longer  than  wide,  while  all  but  a  very  few  specimens  of  C.  mutata  are 
wider  than  long. 

Most  recent  writers  have  referred  this  species  to  the  genus  Pugnax, 
but  a  careful  examination  of  the  internal  characters  shows  such  reference 
to  be  incorrect.  With  the  small  crural  cavity  between  the  bases  of  the 
divided  hinge-plate,  supported  by  a  median  septum,  the  species  must  be 
excluded  from  the  genus  Pugnax. 


LIORIIYNCHUS  185 

The  species  has  sometimes  been  referred  to  Wilscmia,  but  it  differs  from 
members  of  that  genus  in  the  absence  of  longitudinal,  median  grooves 
upon  the  plications  as  they  approach  the  anterior  margin. 

Horizon. — Salem  limestone. 

Genus  LIOBHYNCHUS  Hall 

Description. — Shell  usually  of  about  medium  size,  subovate  in  outline 
and  often  subglobular  in  form.  Mesial  fold  and  sinus  well  developed,  the 
plications  obsolete  or  nearly  obsolete  upon  the  lateral  slopes  of  the  valves, 
more  or  less  well  developed  on  the  fold  and  sinus.  Internal  characters  of 
both  valves  as  in  Camarotcechia. 

Remarks. — This  genus  has  its  greatest  development  in  the  Devonian 
faunas,  but  a  few  species  are  known  in  the  Mississippian.  The  distin- 
guishing characteristic  of  the  genus  is  found  in  the  condition  of  develop 
ment  of  the  plications,  in  combination  with  the  median  septum  and  crural 
cavity  of  the  rostral  portion  of  the  brachial  valve. 

LlORHYNCHUS   GREENIANUM     (Ulrich) 

Plate  XXV,  Figs.  27-33 

1886.     Rhynchonella  greeniana  Ulrich,  Cent,    to    Am.  Pal.,  No.  1,  p.  26, 

pi.  3,  figs,  1-ld. 
1895.     Liorhynchus  Greeniamis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

p.    194. 
1895.     Fugnax  Greenianus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  60, 

figs.  36-38. 
1910.     Leiorliynchus  greeneanum  Weller,  Bull.   Geol.   Soc.  Am.,   vol.   21, 

p.  511,  fig.  12. 

Description.—  Shell  of  medium  size  or  a  little  larger,  subglobular  in 
form,  width  usually  a  little  greater  than  the  length,  the  greatest  width 
near  the  mid-length  of  the  shell,  the  postero-lateral  margins  meeting  at  the 
beak  in  a  rounded  obtuse  angle,  the  lateral  margins  rounded,  the  anterior 
margin  usually  broadly  emarginate.  The  dimensions  of  a  nearly  complete 
specimen  are :    length  28.5  mm.  width  28  mm.,  thickness  24.2  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  the  surface  nearly  flat  from 
just  in  front  of  the  umbo  towards  the  antero-lateral  margins  in  a  broadly 
V-shaped  region,  from  each  limb  of  this  V-shaped  region  the  surface 
curves  abruptly  to  the  postero-lateral  margins  on  the  outside  and  more 
gently  into  the  sinus  internally,  from  the  beak  to  the  front  along  the 
median  line  the  surface  is  arched  to  form  nearly  a  semicircle ;  the  mesial 
sinus  originating  near  the  middle  of  the  valve  as  a  broad,  shallow,  gently 
concave  depression  which  becomes  much  deeper  anteriorly;  it  is  not 
sharply  defined  laterally  and  is  produced  in  front  in  a  broad,  lingual  ex- 
tension, rounded  in  front  and  usually  concave  transversely,  and  whose 


ISI! 


M  [SSISSIPPIAN    BRACHIOPODA 


surface  anteriorly  lies  in  nearly  a  right  angle  to  the  piano  of  the  valve; 
beak  rather  blunt  and  short,  incurved  and  nearly  in  contact  with  the 
umbo  of  the  opposite  valve,  the  delthyrinm  apparently  broadly  triangular 
and  nearly  tilled  by  the  beak  of  the  opposite  valve,  the  deltidial  plates 
and  foramen  obscure  and  not  observed  in  any  of  the  specimens  studied; 
plications  almost  obsolete,  limited  to  from  two  to  four,  all  of  which  are 
present  in  the  anterior  pari  of  the  sinus,  having  their  origin  near  or  in 
front  of  the  middle  of  the  valve.  Internally  the  hinge-teeth  are  sup- 
ported by  a  pair  of  short  dental  plates  which  scarcely  extend  beyond  the 
articulation  of  the  hinge., 


Fig.  7. — A  series  of  seven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Liorhynchus  greenianum  (X  2%),  showing  the  dental  lamellae  in  the  pedicle 
valve  and  the  median  septum  and  crural  cavity  in  the  brachial  valve. 


Brachial  valve  gibbous,  its  convexity  much  greater  than  that  of  the 
pedicle  valve,  the  surface  strongly  arched  from  beak  to  front  along  the 
median  line  with  an  increasing  curvature  towards  the  beak,  laterally  from 
the  median  line  the  surface  curves  abruptly  to  the  margins,  the  curvature 
usually  being  a  little  broken  towards  the  front  by  the  differentiation  of 
the  mesial  fold ;  the  mesial  fold  obsolete  in  the  posterior  half  of  the  valve, 
usually  but  not  always  slightly  differentiated  anteriorly ;  the  beak 
strongly  incurved  beneath  that  of  the  opposite  valve ;  the  plications 
similar  to  those  of  the  opposite  valve  and  restricted  to  the  anterior  portion 
of  the  mesial  fold.  Internally  the  cardinal  process  is  wanting  and  the 
hinge-plate  is  divided;  at  the  apex  of  the  valve  a  divided  median  septum 
is  present,  one  side  of  which  supports  each  side  of  the  divided  hinge-plate 
at  its  initial  point,  the  space  between  the  two  divisions  forming  a  crural 
cavity  which,  however,  is  very  short  and  terminates  before  the  articula- 
tion of  the  hinge  is  reached,  beyond  the  crural  cavity  the  septum  is  rapidly 
reduced  in  height  and  continues  anteriorly  for  from  one-fourth  to  one- 
third  of  the  length  of  the  valve  as  a  faint  ridge. 


PAKYPHORHYTSTCHUS  187 

The  minute  surface  markings  of  the  shell  are  preserved  in  none  of  the 
specimens  studied,  but  concentric  lines  of  growth,  irregular  in  strength 
and  distribution,  are  present  upon  all  specimens  examined. 

E<  marks. — In  its  external  form  this  species  most  closely  resembles 
Shumardella  oosolcns,  but  it  always  grows  to  a  much  larger  size  and  may 
be  recognized  by  that  character  alone.  Internally  the  two  forms  are 
quite  distinct,  L.  greenianum  having  the  hinge  plate  of  the  brachial  valve 
completely  divided,  with  the  space  between  the  two  divisions  of  the 
median  septum  much  broader,  and  the  septum  reduced  in  height  much 
more  rapidly.  Both  the  internal  characters  and  the  external  form  agree 
with  the  genus  IAorhymch/us,  in  which  genus  the  species  is  placed  un- 
hesitatingly. 

Horizon.— Knobstone  formation,  Indiana. 

Gtenus  PARYPHORHYNCHUS  Weller 

Description.— Shells  rhynchonelliform,  of  medium  size  or  larger,  sub- 
ovate  to  transversely  subrhomboidal  in  outline,  mesial  fold  and  sinus 
well  developed,  both  valves  marked  by  broad,  rounded  plications,  which 
reach  nearly  or  quite  to  the  beak,  surface  of  both  valves  also  marked  by 
fine,  radiating  stria?  which  cover  both  the  plications  and  the  intervening 
furrows.  The  internal  characters  of  the  rostral  portion  of  both  valves 
entirely  similar  to  CamarotcccJiia. 


00 


F  G 

Pig.  8. — A  series  of  seven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Paryphorhynchus  elongatum  (X  2%),  showing  the  dental  lamellae  of  the 
pedicle  valve  and  the  median  septum,  crural  cavity  and  crura  of  the  brachial 
valve. 

Remarks.— In  the  arrangement  of  the  internal  structures  of  the  rostral 
portion  of  the  shell  in  this  genus,  there  is  nothing  to  differentiate  it  from 
Camarotcechia.  The  essential  generic  features  are  found  in  the  external 
characters,  viz.,  the  broad  plications  and  especially  in  the  finely  striate 
shell  surface,  in  association  with  the  camarotochoid  interior. 


188  MISSISSIPPI, \.\     HKACIIIOl'om 

PaBYPHOBHYNCHUS   TBANSVERSUM    Well  it 

Plate  XXVI,  Pigs.  23-28 

1895.  Pugnax  missourit  wis  Hal]  and  Clarke,  Pal.  N.  V.,  vol.  8,  pt.  2,  pi.  62, 
figs.  44-4;").     (Not  Bhynckonella  mdssouriensis  Shumard,  1855.) 

1900.  Pugnax  striatocostata  var.?  Weller,  Trans.  St.  Louis  Acad.  Sei., 
vol.   10.   p.  72.  ])!.  2.   figs.   16-17. 

L905.  Paraphorhynchus  trcmsversum  Weller.  Trans.  St.  Louis  Acad.  Sci., 
vol.   lf>,   p.  264,  pi.   1.  figs.   12-15. 

Description. — Shell  of  medium  size,  wider  than  long,  transversely 
SUbelliptical  in  outline,  the  greatest  width  near  the  mid-length,  the  pos- 
terolateral margins  nearly  straight  and  meeting  at  the  beak  in  an  ohtuse 
angle,  the  lateral  and  antero-lateral  margins  rounded,  the  anterior  mar- 
gin gently  convex.  The  dimensions  of  a  nearly  complete  internal  cast 
are:  length  25  nun.,  width  31  mm.,  thickness  23  mm.,  width  of  sinus  in 
front   10.5  mm. 

Pedicle  valve  flattened  hack  of  the  umbo,  the  surface  curving  rather 
abruptly  to  the  posterolateral  margin  and  usually  incurved  to  some  ex- 
tent, to  the  antero-lateral  margins  the  surface  is  gently  convex,  and  to 
the  front  it  is  strongly  arched;  the  mesial  sinus  originates  in  or  near 
the  umbonal  region  and  becomes  rapidly  deeper  towards  the  front;  it  is 
deeply  concave  anteriorly  and  is  produced  in  a  rounded  lingual  extension 
in  front ;  the  beak  is  obtusely  pointed  and  rather  sharply  incurved ;  the 
plications  are  broad,  subangular  or  rounded  on  top  with  furrows  of  about 
equal  width  separating  them,  three  or  more,  usually  four,  are  included 
in  the  sinus  with  about  four  upon  each  lateral  slope  of  the  valve,  some- 
times the  lateral  plications  of  the  sinus  become  obsolete  towards  the  front. 
Internally  the  teeth  are  supported  by  a  pair  of  diverging  dental  lamella^ 
which  extend  anteriorly  from  the  beak  for  about  one-fourth  the  length 
of  the  valve. 

Brachial  valve  much  more  convex  than  the  pedicle,  the  greatest  con- 
vexity at  or  near  the  anterior  margin,  the  surface  sloping  from  the  front 
to  the  beak  along  the  median  line  with  a  gradually  increasing  curvature, 
posteriorly  the  surface  curves  abruptly  towards  the  posterolateral  mar- 
gins and  is  slightly  inflected,  forming  with  the  narrower  incurved  por- 
tion of  the  opposite  valve  a  lateral  concave  region  on  each  side  of  the 
beak ;  mesial  fold  not  differentiated  in  the  umbonal  region,  at  first 
gradually  and  then  more  strongly  elevated  towards  the  front,  convex  on 
top  with  rather  steep  sides,  its  width  in  front  equal  to  nearly  half  the 
width  of  the  shell ;  the  lateral  slopes  curving  strongly  towards  the  oppo- 
site valve  both  laterally  and  anteriorly ;  the  beak  strongly  incurved 
beneath  that  of  the  opposite  valve ;  the  plications  are  similar  in  form  and 
number  to  those  of  the  opposite  valve,  sometimes  the  two  lateral  plications 
of  the  fold  coalesce  with  the  next  inner  ones  towards  the  front.    Internally 


I'AKVIMKIKIIVNCHI'S  189 

there  is  no  cardinal  process,  the  hinge-plate  is  divided  to  the  hase  and 
its  initial  portion  is  supported  by  a  divided  median  septum  forming  a 
crural  cavity  ;i1  the  base  of  the  divided  hinge-plate,  the  median  septum 
continues  with  gradually  decreasing  height  for  about  one-fourth  the  length 
of  the  valve  from  the  beak. 

Tn  addition  to  the  plications  the  surface  is  marked  by  fine  radiating 
stria-,  about  four  of  which  occupy  the  space  of  one  millimeter,  and  by 
concentric  lines  of  growth  which  are  irregular  in  strength  and  distribu- 
tion but  usually  become  more  conspicuous  anteriorly. 

Remarks. — This  species,  so  far  as  known,  is  restricted  in  its  distribution 
to  some  of  the  fine  yellow  sandstone  formations  in  the  Kinderhook  at 
Burlington,  Iowa;  Washington  County,  Iowa;  and  Kinderhook,  Illinois. 
It  is  most  closely  allied  to  P.  striaticostatum,  but  it  attains  a  larger  size 
than  that  species  and  is  proportionally  much  wider  with  a  more  obtuse 
beak.  Some  of  the  young  individuals  have  more  the  outline  of  P. 
striaticostatum,  but  as  they  increase  in  age  they  become  more  transverse. 

Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 

Paetphorhynchus  striaticostatum  (Meek  and  Worthen) 

Plate  XXVI,  Figs.  15-22 

1868.     Bhynchonella  Missouriensis  Meek  and  Worthen,  Geol.  Surv.  111.,  vol. 

3,  p.  450,  pi.  14,  figs.  7a-d. 
1868.     Bhynchonella  striatocostata  Meek    and    Worthen,  Geol.  Surv.  111., 

vol.  3,  p.  452. 
1895.     Pugnax  striato-costata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

p.  204. 
1895.     Pugnax  missouriensis  Hall  and  Clarke,   Pal.  N.  T.,  vol.   8,  pt.  2, 

pi.  60.  figs.  33-34. 
1901.     Pugnax  striatocostata  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 

p.  154,  pi.  13,  figs.  14-16. 
1905.     Paraphorhynchus  slriatocostatum  Weller,   Trans.   St.   Louis  Acad. 

Sci.,  vol.  15,  p.  262,  pi.  1,  figs.  6-11.  . 

Description. — Shell  of  about  medium  size,  broadly  subovate  or  subtrian- 
gular  in  outline,  the  width  usually  greater  than  the  length,  the  greatest 
width  near  or  anterior  to  the  mid-length,  the  postero-lateral  margins 
slightly  convex  or  nearly  straight,  meeting  at  the  beak  in  an  angle  of 
from  80  to  100  degrees,  the  antero-lateral  and  anterior  margins  regularly 
rounded  or  with  the  anterior  margin  sometimes  straightened.  The  dimen- 
sions of  a  nearly  perfect  specimen  are:  length  25  mm.,  width  26  mm., 
thickness  17.8  mm.,  width  of  sinus  in  front  18  mm. 

Pedicle  valve  shallow,  the  surface  flattened  towards  the  umbo,  curving 
abruptly  to  the  postero-lateral  margins  and  sometimes  becoming  some- 
what inflected,  curving  gently  to  the  antero-lateral  margins  and  strongly 
arched  from  beak  to  front ;  mesial  sinus  originating  on  or  close  to  the  um- 
bonal  region,  becoming  deep  and  broad  anteriorly,  rounded  in  the  bottom 


190  U  ississil'i'lAX    BBACH10PODA 

and  produced  in  front  in  a  broad,  rounded,  lingual  extension  whose  sur- 
face ;il  the  front  of  adult  shells  lies  in  dearly  a  right  angle  to  the  plane  of 
the  valve  ;  beak  small,  pointed,  incurved  so  as  to  lie  almost  in  contact  with 
the  umbo  of  the  opposite  valve  in  full  grown  specimens,  pierced  at  the 
apex  by  a  x^vy  small  subcircular  foramen;  delthyrium  broadly  triangular, 
nearly  filled  by  the  beak  of  the  opposite  valve,  the  deltidial  plates  incon- 
spicuous; plications  coarse  and  strong,  rounded,  with  furrows  oi'  about 
equal  width  between,  three  or  four  plications  are  usually  present  in  the 
bottom  of  the  broad  sinus  and  three  or  four  upon  each  Lateral  slope,  mak- 
ing from  nine  to  twelve  upon  the  entire  valve,  the  one  nearest  the  postero- 
lateral margin  on  each  side  usually  being  faint  or  obscure.  Internally 
the  teeth  are  supported  by  a  pair  of  dental  lamellae  which  diverge  ante- 
riorly and  continue  for  about  one-fifth  of  the  length  of  the  valve. 

Brachial  valve  much  more  convex  than  the  pedicle,  the  greatest  depth 
at  or  near  the  anterior  margin,  the  surface  sloping  with  a  gradually  in- 
creasing curvature  from  the  anterior  margin  to  the  beak,  from  the  median 
line  the  surface  curves  abruptly  to  the  postero-lateral  margins  and  towards 
the  beak  is  sometimes  a  little  inflected  as  it  approaches  the  margin  to 
form,  with  a  similar  inflected  portion  of  the  opposite  valve,  an  ill-defined, 
slightly  concave,  lateral  area  on  each  side  of  the  valve,  in  the  anterior 
portion  of  the  valve  the  surface  passes  from  the  median  line  with  an  ab- 
rupt double  curvature,  first  to  the  border  of  the  mesial  fold  and  then  to 
the  lateral  margins  of  the  valve ;  the  mesial  fold  is  ill-defined  posteriorly 
but  originates  back  of  the  middle  of  the  valve  and  is  strongly  elevated  in 
front  where  it  is  broad  and  rounded  on  top ;  the  beak  is  strongly  incurved 
beneath  that  of  the  opposite  valve,  the  plications  correspond  in  form  and 
number  to  those  of  the  opposite  valve  with  which  they  alternate.  Inter- 
nally there  is  no  cardinal  process  and  the  hinge-plate  is  divided  to  the 
base,  being  supported  in  its  initial  portion  by  a  median  septum  which  di- 
vides to  form  a  crural  cavity  between  the  two  divisions  of  the  hinge-plate 
as  in  the  genus  C '  amarotozchia. 

In  addition  to  the  plications  the  surface  of  both  valves  is  marked  by 
fine,  radiating,  longitudinal  stri&\  about  four  or  five  of  which  occupy  the 
space  of  one  millimeter  and  by  fine  concentric  lines  of  growth.  On  some 
examples  stronger  lines  of  growth  are  sometimes  present  at  intervals. 

Remarks.  —  This  species  can  be  easily  distinguished  from  the  other  mem- 
beers  of  the  genus  Parypliorhynchus,  by  its  smaller  size  and  somewhat  in- 
termediate character,  it  being  distinctly  shorter  than  P.  elongatum  and 
narrower  than  P.  tramversuni.  The  species  occurs  most  commonly  in  bed 
No.  4  of  the  Kinderhook  section  at  Burlington,  Iowa,  and  in  a  Kinderhook 
limestone  near  Kinderhook-  Pike  County,  Illinois.  The  recorded  occur- 
rence of  the  species  in  the  Louisiana  limestone  of  Missouri  is  probably  an 
error. 

Horizon.— Kinderhook. 


PARYPIIORIIYNCHUS  191 

Paryphoriiynchus  elongatum  Weller 
Plate  XXVI,  Figs.  10-14 

190f).     Paraphorhynchus  elongatum   Weller,  Trans.  St.  Louis  Acad.  Sci., 
vol.  15,  p.  216.  pi.  1,  figs.  1-5. 

Description.— Shell  of  medium  size  or  larger,  subovate  in  outline,  longer 
than  wide,  the  greatest  width  anterior  to  the  middle,  the  postero-lateral 
margins  nearly  straight  or  gently  convex  and  meeting  at  the  beak  in  an 
acute  angle  of  from  70  to  85  degrees,  the  anterior  and  antero-lateral  mar- 
gins rounded.  The  dimensions  of  a  nearly  perfect  specimen  are :  length 
of  pedicle  valve  37  mm.,  length  of  brachial  valve  34.7  mm.,  width  28.8  mm., 
thickness  22.5  mm.,  width  of  sinus  in  front  23.8  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  near  or  posterior 
to  the  middle,  posteriorly  the  surface  is  regularly  convex  transversely  in 
the  central  portion  of  the  valve,  but  as  it  approaches  the  lateral  margins 
it  curves  rather  abruptly  towards  the  opposite  valve  and  is  then  continued 
in  a  nearly  vertical  or  slightly  inflected  direction  to  the  edge,  from  the 
beak  to  the  front  the  surface  describes  nearly  a  semicircle  in  full  grown 
shells,  but  to  the  antero-lateral  margins  the  curvature  is  not  so  great ;  the 
mesial  sinus  originates  near  the  middle  of  the  valve  and  is  formed  rather 
by  the  elevation  of  the  borders  above  the  general  surface  of  the  valve 
than  by  the  distinct  depression  of  the  sinus  itself,  it  is  broad  and 
is  gently  convex  transversely  across  the  depressed  portion,  anteriorly  it 
is  produced  as  a  broad,  rounded,  lingual  extension  whose  surface  at  the 
extreme  margin  lies  at  nearly  a  right  angle  to  the  general  plane  of  the 
valve ;  the  lateral  slopes  are  narrow  and  are  abruptly  elevated  from  the 
bottom  of  the  sinus  in  front;  the  beak  is  small,  sharply  pointed,  closely 
incurved  and  nearly  in  contact  with  the  umbo  of  the  opposite  valve;  the 
delthyrium  is  broadly  triangular  and  is  nearly  filled  by  the  beak  of  the 
opposite  valve,  neither  the  deltidial  plates  nor  the  foramen  has  been  ob- 
served, but  both  must  be  inconspicuous;  the  plications  originate  near  the 
beak  and  are  broad  and  rounded  on  top  with  rounded  furrows  of  about 
equal  width  between,  they  are  from  ten  to  fourteen  in  number,  four  or 
five  of  which  occupy  the  sinus,  the  outermost  plication  of  the  sinus  on 
each  side  frequently  becomes  obsolete  before  it  reaches  the  anterior  mar- 
gin. Internally  the  teeth  are  supported  by  a  pair  of  strong  dental  lam- 
ella' which  may  extend  anteriorly  from  the  beak  from  one-fifth  to  one- 
fourth  the  length  of  the  valve.  Upon  the  casts  of  the  interior  of  the 
valve  well  defined  but  delicate  pallial  sinuses  are  clearly  shown. 

Brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  the 
greatest  depth  at  or  near  the  anterior  margin,  the  surface  curving  from 
the  anterior  margin  to  the  beak,  along  the  median  line,  with  a  gradually 
increasing  curvature  which  becomes  rather  abrupt  near  the  beak;  in  the 


l!r_»  MISSISSII'I'IAN    liKACHIOPODA 

median  portion  of  the  valve,  posteriorly,  the  surface  is  regularly  convex 
transversely,  but  near  Hie  postero-lateral  margins  it  curves  rather  ab- 
ruptly towards  the  opposite  valve  and  (hen  continues  in  a  nearly  vertical 
direction  to  the  margin  where  it  meets  the  similar  vertical  surface  of  the 
opposite  valve  and  forms  the  Lateral  flattened  or  slightly  concave  region 
which  is  present  each  side  of  the  beak;  the  mesial  fold  is  obsolete  in  the 
umbonal  region,  is  gradually  elevated  anteriorly  to  Dear  the  front  margin 
where  the  elevation  becomes  abrupt,  or  rather  the  lateral  slopes  are 
curved  abruptly  towards  the  opposite  valve,  the  fold  is  sharply  defined 
and  is  marly  flat  or  slightly  convex  transversely  across  the  top  with  ab- 
ruptly descending  sides;  the  lateral  slopes  of  the  valve  are  narrow,  their 
surface  curves  gently  from  the  sides  of  the  fold  towards  the  lateral  mar- 
gins for  a  short  distance  and  then  curves  abruptly  towards  the  opposite 
valve;  the  beak  is  incurved  strongly  beneath  that  of  the  opposite  valve; 
the  plications  are  similar  in  form  and  number  to  those  of  the  opposite 
valve,  one  or  more  pairs  upon  the  fold  sometimes  coalescing  as  they  ap- 
proach the  anterior  margin.  Internally  no  cardinal  process  is  present 
and  the  hinge-plate  is  divided  to  the  base,  each  division  being  supported 
by  one  side  of  a  crural  cavity  which  is  joined  to  the  floor  of  the 
valve  by  a  median  septum,  the  crural  cavity  continues  to  a  point  opposite 
the  articulation  of  the  hinge,  beyond  which  the  median  septum  becomes 
rapidly  lower,  the  crura  extend  forward  into  the  cavity  of  the  shell  from 
the  anterior  margin  of  the  hinge-plate. 

In  addition  to  the  plications  the  surface  of  each  valve  is  marked  by 
fine  radiating  striae,  four  or  five  of  which  occupy  the  space  of  one  milli- 
meter, and  by  still  finer  concentric  striae  with  stronger  lines  of  growth  at 
intervals. 

Remarks. — In  some  of  its  aspects  this  species  resembles  the  elongate, 
coarsely  plicated  shells  of  Bhynchotetra  caput-testudinis  with  its  flattened 
lateral  areas  on  each  side  of  the  beak,  but  it  is  smaller  than  that  species 
and  more  distinctly  striated  longitudinally  besides  possessing  an  entirely 
different  internal  structure,  there  being  no  median  septum  and  spondy- 
lium  in  the  pedicle  valve.  The  species  differs  from  P.  striaticostatum  in  its 
larger  size,  more  elongate  form,  more  convex  valves  and  the  more  con- 
spicuous, lateral,  flattened  areas  on  each  side  of  the  beak. 

Horizon. — Kinderhook. 

Genus  PUGNOIDES  Weller 

Description.  —  Shells  rhynchonelliform,  below  medium  size,  subovate  in 
outline,  with  the  fold  and  sinus  well  developed.  Both  valves  marked  by 
rounded  or  subangular  plications  which  become  obsolete  in  the  posterior 
portion  of  the  shell.  Internal  characters  of  both  valves  essentially  as  in 
Camarotcechia. 


PUGNOIDES  193 

Remarks. — This  genus  approaches  more  closely  to  Cmnarotcechia  than 
any  of  those  here  considered,  having  camarotoechoid  interiors,  although 
the  genotype  has  usually  been  included  in  Pugnax,  in  which  no  median 
.septum  or  crural  cavity  is  developed  in  the  rostral  portion  of  the  brachial 
valve.  The  members  of  this  genus  agree  with  Camarotoechia  in  general 
size,  and  form,  as  well  as  in  internal  characters,  being  distinguished  from 
that  genus  by  the  obsolescence  of  the  plications  towards  the  beak,  in  which 
character  they  are  like  Pugnax. 

PUGNOIDES   OTTUMWA    (White) 

Plate  XXV,  Figs.  7-17 

1862.     Ehynchonella  Ottumwa  White,  Proc.  Bost.  Soc.  Nat.  Hist.,  vol.  9, 

p.  23. 
1880.     Ehynchonella  ottumwa  White,   Cont.  to  Inv.  Pal.,  No.  8,  p.   165, 

pi.  41,  figs.  5a-c. 

1894.  Ehynchonella  ottumwa  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  103. 

1895.  Pugnax  Ottumwa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  60, 

figs.  23-26. 
1910.     Pugnoicles  ottumwa  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21,  p.  512, 
fig.  13. 

Description.—  Shell  below  medium  size,  suboval  to  subpentagonal  in 
outline,  usually  wider  than  long,  the  greatest  width  usually  anterior  to 
the  mid-length  of  the  shell.  The  dimensions  of  two  individuals  are: 
length  12  mm.  and  10.7  mm.,  width  12.5  mm.  and  11.3  mm.,  thickness  8 
mm.  and  6.3  mm. 

Pedicle  valve  with  rather  long,  nearly  straight  postei'o-lateral  margins 
which  meet  at  the  beak  in  an  acute  angle,  the  lateral  and  anterior  mar- 
gins rounded,  the  surface  convex  in  the  umbonal  region,  curving  abruptly 
to  the  postero-lateral  margins,  less  abruptly  to  the  anterior  margin  and 
only  gently  convex  or  nearly  straight  to  the  antero-lateral  margins ;  along 

o    o    o    <Q>   <ty   <£}> 

G  M  |  j  K 

Fig.  9. — A  series  of  eleven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Pugnoidcs  ottumwa  (X  2%),  showing  the  dental  lamellae  of  the  pedicle  valve 
and  the  median  septum,  crural   cavity  and  crura  of  the  brachial  valve. 

the  postei'o-lateral  margins  towards  the  beak,  the  edge  of  the  valve  is  ab- 
ruptly inflected  to  form  a  sort  of  false  cardinal  area ;  mesial  sinus  obso- 

—7 


194  m  issfssi  I'l'l  A  N    BBACHIOFODA 

lete  in  the  posterior  half  of  the  valve,  becoming  rather  broad  and  deep 
anteriorly  and  somewhal  produced  in  front  in  a  linguiform  extension 
which  curves  strongly  towards  the  opposite  valve;  the  beak  acutely 
pointed,  only  a  little  incurved,  produced  posteriorly  beyond  the  brachial 
valve  to  a  conspicuous  degree;  delthyrium  Large  and  triangular,  partially 
dosed  by  a  pseudo-delt  idiuni,  with  a,  large,  subelliptical  foramen;  plica- 
tions simple,  obsolete  towards  the  beak  bnl  originating  iii  or  near  the 
uuibonal  region,  gradually  increasing  in  strength  until  they  become  con- 
spicuously subangular  towards  the  margin,  usually  two  or  three  are  pres- 
ent in  the  bottom  of  the  sinus,  more  rarely  one,  four  or  five,  upon  each 
lateral  slope  there  are  usually  Ihree  but  sometimes  only  two  strong  pli- 
cations, with  from  one  to  four  additional  weaker  ones  towards  the  car- 
dinal margin.  Internally  the  teeth  are  supported  by  a  pair  of  short  dental 
plates. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  from  the  center  of  the  valve  the  surface  curves  most 
abruptly  to  the  post  cm- lateral  margins,  more  gently  to  the  posterior 
extremity  and  to  the  anterolateral  margins,  and  extends  nearly  horizon- 
tally to  the  anterior  margin;  mesial  fold  obsolete  posteriorly,  becoming 

s< what  strongly  elevated  in  front;  the  beak  incurved  beneath  that  of 

the  opposite  valve;  plications  entirely  similar  to  those  of  the  opposite 
valve,  three  or  four  usually  present  on  the  fold-  but  sometimes  two  or 
five,  two  or  three  strong  ones  on  each  lateral  slope,  and  several  weaker 
ones.  Internally  the  valve  bears  a  median  septum  which  is  somewhat 
rapidly  reduced  in  elevation  in  passing  from  the  beak  anterioi'ly,  becom- 
ing entirely  obsolete  in  about  one-third  or  less  the  length  of  the  valve, 
posteriorly  the  septum  is  divided  to  form  a  crural  cavity  which  does  not 
continue  anteriorly  beyond  the  hinge  sockets,  each  side  of  the  divided 
septum  is  produced  anteriorly  into  one  of  the  lateral  divisions  of  the  hinge 
plate,  and  these  in  turn  are  produced  into  the  somewhat  elongate  crura 
which  curve  towards  the  pedicle  valve. 

Surface  of  both  valves  usually  quite  smooth  aside  from  the  plications, 
except  near  the  margin  of  adult  shells  where  there  may  be  several  more 
or  less  distinct  lines  of  growth,  sometimes  a  more  or  less  distinct  line  of 
growth  is  present  in  the  umbonal  region  and  when  present  it  usually 
marks  the  place  of  origin  of  the  plications. 

Remarks. — This  shell  is  usually  a  prolific  species  wherever  it  is  found. 
It  occurs  most  abundantly  in  the  Pella  beds  of  Iowa,  but  is  also  a  con- 
spicuous species  in  some  of  the  Ste.  Genevieve  beds  of  Illinois.  The 
species  may  be  easily  recognized  by  its  smooth  shell,  aside  from  the  plica- 
tions, by  the  conspicuously  protuberant  beak  of  the  pedicle  valve,  and  by 
the  inflected  cardinal  margin  of  the  pedicle  valve  to  form  a  false  cardinal 
area. 


PUGNOIDES  195 

The  species  has  been  referred  to  the  genus  Pugnax  by  Hall  and  Clarke, 
but  the  interna]  structure  of  the  brachial  valve  is  that  of  Camarotoechia 
rather  than  Pugnax.  The  specimen  figured  by  these  authors  as  the 
brachial  valve  of  the  species  with  its  broadly  divided  hinge-plate  unsup- 
ported by  a  median  septum,  must  be  either  incomplete  or  it  must  be  some- 
thing else.  Repeated  sections  of  authentic  examples  from  Fella,  Iowa, 
show  the  camerotoechoid  characters  here  described  and  illustrated. 

Horizon. — Ste.  Genevieve  limestone. 

PUGNOIDES  BOONENSIS   (Shumai'd) 

Plate  XXV,  Figs.  22-26 

1855.     Rhynchonella  Boonensis  Shumard,  Geol.  Rep.  Mo.,  p.  205,  pi.  C, 
figs.  6a-b. 

1894.  Rhynchonella  boonensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  101. 

1895.  Leiorhynchus   (?)   Boonensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8, 

pt.   2,   pi.    60,   fig.    35. 

Description. — Shell  of  about  medium  size,  broadly  ovate-subtriangular 
in  outline,  wider  than  long,  the  greatest  width  near  the  mid-length,  the 
postero-lateral  margins  nearly  straight  and  meeting  in  an  obtuse  angle, 
the  antero-lateral  margins  rounded,  the  anterior  margin  sinuate.  The 
dimensions  of  a  nearly  perfect  specimen  are :  length  of  pedicle  valve 
19.1  mm.,  length  of  brachial  valve  17.9  mm.,  greatest  width  24  mm., 
thickness  17  mm.,  width  of  mesial  sinus  of  pedicle  valve  in  front  17  mm. 

Pedicle  valve  gently  convex  in  the  umbonal  region,  flattened  towards 
the  antero-lateral  margins,  strongly  arched  from  beak  to  front  along 
the  median  line,  the  curve  forming  nearly  a  semicircle,  narrowly  but 
rather  abruptly  curved  along  the  postero-lateral  margins  and  a  little 
inflected  to  the  cardinal  extremities ;  mesial  sinus  originating  near  the 
mid  length  of  the  valve,  becoming  broad  and  rather  deep  anteriorly 
and  produced  in  a  broadly  rounded  lingual  extension  whose  surface  lies 
at  nearly  a  right  angle  to  the  plane  of  the  valve ;  the  beak  obtusely  pointed 
and  only  a  little  incurved ;  plications  obsolete  upon  the  posterior  portion 
of  the  valve,  but  a  little  developed  in  front  of  the  middle,  those  of  the 
sinus,  two  in  number,  originating  near  the  mid-length  of  the  valve, 
rounded  on  top  and  becoming  stronger  towards  the  anterior  margin,  on 
one  or  both  sides  of  this  pair  of  strong  plications  there  is  sometimes  a 
much  fainter  plication  initiated  near  the  margin ;  on  each  side  of  the 
mesial  sinus  upon  the  lateral  slopes  one  or  two  faint  plications  are  com- 
monly present  which  are  limited  to  the  extreme  margin  of  the  valve. 
Internally  the  dental  lamella  are  short,  between  them  in  the  rostral  por- 
tion of  the  valve  is  a  short,  low,  median  ridge,  but  anteriorly,  beyond  the 
extremities  of  the  lamella1  the  inner  surface  of  the  valve  is  somewhat 
excavated  for  the  muscular  attachment. 


L96 


MISSISSII'I'lAN     HHACIIlOl'OliA 


Brachial  valve  strongly  convex  transversely  and  moderately  convex 
from  ilif  beak  to  near  the  fronl  along  the  median  line,  the  greatest  con- 
vexity of  the  valve  near  the  Eronl  margin,  the  anterior  slope  very  short 
and  curving  somewhal  abruptly  to  the  anterior  margin;  mesial  fold  not 

differentiated   IV Hie  general  convexity  except   towards  the  anterior 

margin,  and  even  there  the  differentiation  is  not  conspicuous;  the  beak 
pointed  and  incurved  beneath  the  beak  of  the  opposite  valve;  three  short 
hut  rather  strong  plications  are  present  anteriorly  upon  the  mesial  fold, 
and   one  or  two   fainter  and  even   shorter  ones  upon   each   lateral  slope, 


£8$ 


<n> 

CD 


Pig.  10.— A  series  of  six  cross-sections  of  the  rostral  portion  of  the  shell  of 
Pugnoides  boonensis  (X  2%),  showing  the  dental  lamellae  and  slight  median 
septum  of  the  pedicle  valve,  and  the  median  septum,  the  small  crural  cavity 
and  the  crura  of  the  brachial  valve. 

the  greater  portion  of  the  valve  posteriorly  entirely  non-plicate.  In- 
ternally a  well  developed  median  septum  is  present  which  extends  an- 
teriorly upon  the  interior  surface  of  the  valve  for  more  than  one-third 
the  length  of  the  valve,  in  the  rostral  portion  of  the  valve  the  median 
septum  is  divided  internally  to  form  a  crural  cavity  such  as  is  present  in 
this  genus,  the  crural  cavity  is  very  short  and  terminates  posterior  to  the 
articulations  of  the  valves,  the  crural  bases  joined  to  the  hinge-plate  for  a 
short  distance  beyond  the  termination  of  the  crural  cavity. 

Surface  of  both  valves  marked  by  fine,  obscure,  but  rather  regular, 
concentric  lines  of  growth,  with  an  occasional  stronger  and  more  or  less 
conspicuous  one ;  radiating  stria?  not  present. 

Remarks.— This  species  approaches  the  European  Pugnax  pugnus  more 
nearly  in  its  external  form  than  any  other  of  our  American  Mississippian 
rhynchonelloids,  but  the  internal  characters  of  the  shell  differentiate  it 


ALLORHYNCHUS  197 

from  the  genus  Pugnax  and  bring  it  in  conformity  with  the  members 
of  the  genus  Pugnoidcs  which  possess  the  median  septum  in  the  brachial 
vave  and  the  crural  eavty  between  the  opposite  parts  of  the  divided  hinge- 
plate.  The  species  is  one  of  the  rarest  forms  in  the  lower  Burlington  lime- 
stone. 

Horizon. — Fern  Glen  formation,  lower  Burlington  limestone. 

Genus  ALLORHYNCHUS  Weller 

Description.— Shells  rhynchonelliform,  small  or  below  medium  size,  with 
mesial  fold  and  sinus  well  developed  and  both  valves  mai-ked  by  sub- 
angular  or  rounded  plications  which  are  usually  well  defined  to  the  beak. 
Interior  of  the  pedicle  valve  with  slender  dental  lamellae.  In  the  brachial 
valve  the  hinge-plate  is  divided,  the  inner  edges  of  each  lateral  portion 
being  unsupported,  no  median  septum  and  no  crural  cavity,  such  as  is 
present  in  Camarotcechia  are  developed. 

Remarks. — In  external  features  the  members  of  this  genus  are  not  essen- 
tially different  from  Camarotcechia,  but  an  examination  of  the  interior 
of  the  rostral  portion  of  the  brachial  valve  shows  that  they  are  not  at  all 
alike.  In  the  entire  absence  of  lamellae  of  any  sort  for  the  support  of  the 
hinge-plate  of  the  brachial  valve,  Allorhynchus  is  like  Pugnax,  but  it 
differs  from  that  genus  in  the  completely  plicated  shell. 

Allorhynchus  heteropsis   (Winchell) 

Plate  XXIV,  Figs.  73-81 

1865.  Rhynchonclla  heteropsis  Win.,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  121. 
1901.     Camarotoechia  ( ?)  heteropsis  Weller,  Trans.  St.  Louis  Acad.  Sci., 

vol.  11,  p.  156,  pi.  13,  figs.  9-13. 
1910.     Allorhynchus  heteropsis  Weller,  Bull.    Geol.    Soc.  Am.,  vol.  21,  p. 

509,  fig.  8. 

Description.  —  Shell  small,  triangularly  subovate  in  outline,  usually  wider 
than  long,  the  greatest  width  anterior  to  the  mid-length  of  the  shell,  the 
postero-lateral  margins  nearly  straight  or  a  little  sigmoidal  and  meeting 
at  the  beak  in  an  angle  from  90  to  108  degrees,  the  antero-lateral  margins 
rounded  and  the  anterior  margin  straight  or  convex.  The  dimensions  of 
two  individuals  are:  length  11.1  mm.  and  12  mm.,  width  13.6  mm.  and 
12  mm.,  thickness  7.5  mm.  and  6.4  mm.,  width  of  sinus  in  front  9.3  mm. 
and  7  mm. 

Pedicle  valve  convex  on  the  umbo,  the  surface  curving  rather  abruptly 
to  the  cardinal  margin  with  the  edges  of  the  valve  narrowly  inflected  for 
a  short  distance  on  each  side  of  the  beak,  towards  the  antero-lateral 
margins  the  surface  is  gently  convex  or  flattened  and  from  the  beak  to 
the  front  margin  it  is  rather  strongly  arched ;  the  sinus  originates  near 


198  MISSISSIITIAN   BRACHIOPODA 

or  a  little  back  of  the  middle  of  the  valve  ami  becomes  rapidly  deeper 

anteriorly  ami  is  moderately  produced  in  a  broad,  r <\rd  extension  in 

front,  where  its  width  is  about  one-half  the  total  width  of  the  shell;  it  is 
usually  nearly  flat  across  the  bottom  in  front  with  the  sides  sloping  out- 
ward or  rarely  nearly  vertical;  the  beak  is  acuminate  and  sharply  pointed 
and  is  strongly  incurved,  coining  nearly  in  contact  with  the  umbo  of  the 
opposite  valve;  the  delthyriuin  is  nearly  tilled  by  the  beak  of  the  opposite 
valve,  the  deltidial  plates  ami  foramen  are  obscure  and  have  not  been 
clearly  recognized  in  any  of  the  specimens  studied;  the  plications  are 
simple,  angular,  rather  coarse,  and  originate  at  the  beak,  three  or  rarely 
four  occupy  the  bottom  of  the  sinus  with  sometimes  an  additional  one 
upon  each  sloping  side,  with  from  four  to  six  upon  each  lateral  slope 
of  the  valve,  the  plications  of  the  lateral  slopes  nearest  the  margins  of  the 
sinus  are  the  strongest  and  most  angular  ones  on  the  valve.  Internally 
the  hinge-teeth  are  weak  and  are  supported  by  a  pair  of  short,  thin, 
dental   lamella-. 

f>  o  o  q  q  q 

F 

Fig.  11. — A  series  of  six  cross-sections  of  the  rostral  portion  of  the  shell  of 
Allorhynchus  heteropsis  (X  2%),  showing  the  presence  of  dental  lamellae  in 
the  pedicle  valve  and  the  entire  absence  of  lamellae  in  the  brachial  valve. 

Brachial  valve  much  more  convex  than  the  pedicle,  its  greatest  convex- 
ity at  or  near  the  front  margin,  the  surface  slopes  along  the  median 
portion  of  the  shell  from  the  front  margin  to  the  beak  with  a  regular  or 
with  an  increasing  curvature,  at  the  umbo  the  surface  is  impressed  along 
the  median  line  in  a  shallow  but  distinct  sinus  which  continues  to  the 
middle  of  the  valve  either  as  a  distinct  sinus  or  as  a  flattened  surface,  to 
the  postero-lateral  margns  the  surface  slopes  first  with  a  convex  curvature 
and  then  becomes  flattened  or  sometimes  even  concave;  the  mesial  fold 
is  scarcely  distinct  back  of  the  middle  of  the  valve  but  anteriorly  it  is 
rather  strongly  and  abruptly  elevated  above  the  lateral  slopes;  the 
lateral  slopes  are  convex  with  the  surface  curving  rather  strongly  both 
anteriorly  and  laterally ;  the  beak  strongly  incurved  beneath  that  of 
the  opposite  valve ;  the  plications  are  similar  in  form  and  number  to  those 
of  the  opposite  valve.  Internally  the  hinge-plate  is  divided  to  its  base 
and  lacks  supporting  septa  of  any  kind,  the  cardinal  process  and  median 
septum  wanting. 

Remarks. — In  its  usual  condition  of  preservation  the  surface  of  this 
species  is  exfoliated  so  that  all  indication  of  minute  surface  markings  is 
destroyed,  but  upon  remnants  of  the  shell  which  are  sometimes  present 


ALLORHYNCHUS  199 

extremely  fine,  crowded  concentric  striaa  can  be  detected.     Occasionally 
stronger  lines  of  growth  are  present,  but  they  are  never  conspicuous. 
Horizon. — Kinderhook. 

Allokhynchus  macra  (Hall) 

Plate  XXV,  Figs.  1-6 

1856.     Rhynchonella  macra  Hall.  Trans.  Albany  Inst.,  vol.  4,  p.  11. 
1856.    Rhynchonella  ricinula  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  9. 
1882.     Rhynchonella  macra  Whitfield,  Bull.  Am."  Mus.  Nat.  Hist.,  vol.  1, 
p.  52,  pi.  6,  figs.  40-42. 

1882.  Rynchonella  ricinula  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

p.  53,  pi.  6,  fig.  46. 

1883.  Rynchonella  macra  Hall,  12th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  334, 

pi.   29,   figs.  40-42. 
1883.     Rynchonella  ricinula  Hall,  12th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  330, 

pi.   29,   fig.  46. 
1906.     Rhynchonella  macra  Beede,  30th  Ann.  Rep.   Geol.   Surv.  Ind.,  p. 

1307,  pi.    22,   figs.   40-42. 

1906.     Rynchonella  ricinula  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p. 

1308,  pi.  22,  fig.  46. 

1910.     Allorhynchus  macra  Weller,  Bull.  Geol.  Soc.  Am.,  vol  21,  p.  509, 
fig.    9. 

Description.— Shell  small,  compressed,  subovate  to  subtriangular  in 
outline,  usually  a  little  wider  than  long  but  sometimes  longer  than  wide, 
especially  in  small  or  young  individuals,  the  greatest  width  anterior  to  the 
middle,  the  postero-lateral  margins  gently  convex  or  nearly  straight  and 
usually  meeting  at  the  beak  in  an  angle  of  less  than  90  degrees,  the 
antero-lateral  and  anterior  margins  regularly  rounded  or  with  the  an- 
terior margin  sometimes  straigbtened.  The  dimensions  of  two  individuals 
are:  length  6.5  mm.  and  5.5  mm.,  width  7.1  mm.  and  6  mm.,  thickness  3 
mm.  and  2.7  mm.,  width  of  sinus  in  front  4.5  mm.  and  3.1  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  gently 
arched  from  beak  to  front  and  also  transversely  along  the  line  of  greatest 
width,  but  posteriorly  the  curvature  to  the  lateral  margins  is  more 
abrupt,  towards  the  beak  the  edge  of  the  shell  along  the  postero-lateral 
margins  is  abruptly  and  sharply  inflected  to  form  a  rather  conspicuous 
pseudo-cardinal  area;  mesial  sinus  entirely  obsolete  posteriorly  where  it 
is  replaced  by  a  slight  mesial  elevation  which  is  not  differentiated  later- 
ally from  the  lateral  slopes  of  the  valve,  towards  the  front  the  mesial 
portion  of  the  valve  is  somewhat  flattened  and  is  rarely  slightly  de- 
pressed in  a  broad,  shallow,  ill-defined  sinus;  the  beak  is  pointed,  scarcely 
incurved  and  is  produced  posteriorly  rather  conspicuously  in  a  nearly 
horizontal  direction;  the  delthyrium  is  broadly  triangular  and  is  partially 
closed  by  deltidial  plates  which  are  pierced  at  the  apex  by  a  subelliptical 
foramen  which  encroaches  to  some  extent  upon  the  beak  of  the  valve; 


'JW  MISSISS1PPIAN   BBACHIOPODA 

plications  simple,  rounded,  14  to  22  in  number,  two  or  three  of  which  on 
each  side  adjacent  to  the  postero-cardinal  margins  are  very  faint,  they 
are  obsolete  at  the  beak  but  originate  in  the  umbonal  region,  usually  at 
the  firsl  strong  concentric  line  of  growth.  Internally  the  hinge-teeth  are 
supported  by  a  pair  of  short  denial  lamella  which  do  not  extend  anteriorly 
beyond  the  articulation  of  the  hinge. 

?       ?        f         © 

c  D 

Pig.  12. — A  series  of  four  cross-sections  of  the  rostral  portion  of  the  shell  of 
Allot  hum  hits  mm  ni  (x  2*4).  showing  the  dental  lamellae  of  the  pedicle  valve 
and  the  absence  of  lamellae  in  the  brachial  valve. 

Brachial  valve  equally  or  a  little  less  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  anteriorly  the  surface  curves 
gently  to  the  anterior  and  antero-lateral  margins;  posteriorly  the  surface 
first  curves  gently  from  the  median  line  laterally  and  then  rather  abruptly 
as  it  approaches  the  postero-lateral  margins ;  mesial  fold  obsolete ;  in 
younger  specimens  and  in  the  older  part  of  mature  ones  there  is  a  distinct 
but  slight  depression  along  the  median  line  which  continues  to  the  front 
of  full  grown  examples  as  a  broad  mesial  flattening  which  is  not  sharply 
differentiated  from  the  lateral  slopes  of  the  valve ;  the  beak  is  rather 
sharply  incurved  beneath  that  of  the  opposite  valve ;  the  plications  are 
entirely  similar  in  form  and  number  to  those  of  the  opposite  valve.  In- 
ternally the  hinge-plate  is  divided  to  the  base  and  no  median  septum  is 
present,  anteriorly  the  two  divisions  of  the  hinge-plate  are  produced 
as  crura. 

The  surface  of  both  valves,  in  addition  to  the  plications,  is  marked  by 
exceedingly  fine  concentric  stria?  and  by  several  stronger  lines  of  growth 
which  are  sometimes  placed  at  nearly  regular  intervals  throughout  the 
entire  length  of  the  shell,  the  plications  commonly  originate  at  the  first 
of  the  lines  of  growth  in  front  of  the  beak. 

Remarks. — This  species  may  be  easily  recognized  by  its  small  size  and 
much  compressed  shell.  The  smaller  examples  may  sometimes  resemble 
the,  young  of  the  associated  Camarotcechia  mutata,  but  that  species  is 
apt  to  have  a  more  pronounced  sinus  in  the  anterior  margin  of  the  pedicle 
valve,  and  the  internal  characters  of  the  two  species  are  different,  the 
median  septum  of  the  brachial  valve  with  its  crural  cavity  sup- 
porting the  bases  of  the  divided  hinge-plate  being  absent  in  the  present 
species.  RhyncJumella  rici)ntla  Hall,  seems  to  be  only  the  young  of  the 
larger  R.  macra,  and  is  so  considered  here,  although  Whitfield  states  that 
mature  examples  of  R.  macra  do  not  occur  with  R.  rici/nula.  In  the  col- 
lections from  the  Salem  limestone  above  Alton,  Illinois,  the  typical  locality 
for  R.  macra,  small  examples  which  seem  to  agree  fully  with  the  figures 


ALLORHYNCHUS  201 

of  B.  ricinula  are  not  infrequent,  and  their  association  is  such  as  to  in- 
dicate that  they  are  without  doubt  the  young  of  the  larger  examples 
which  more  typically  represent  11.  macra.  These  two  names  were  both 
proposed  by  Hall  in  the  same  paper,  and  as  ricinula  occurs  on  an  earlier 
page  it  might  be  given  priority  by  some,  but  as  no  injustice  can  be  done 
by  adopting  macra  it  seems  best  to  do  so  since  that  name  was  applied 
to  the  mature  and  more  normal  form  of  the  species. 
Horizon. — Salem  limestone. 

Allorhynchus  acuttplicatum  n.  sp. 
Plate  XXIV,  Figs.  83-86 

Description.— Shell  small,  broadly  subovate  in  outline,  broader  than 
long,  the  greatest  width  anterior  to  the  mid-length  of  the  shell,  the 
postero-lateral  margins  nearly  straight  and  meeting  at  the  beak  in  an 
angle  of  about  90  degrees  or  a  little  more,  the  antero-lateral  margins 
rounded,  the  anterior  margin  usually  nearly  straight  but  sometimes  slight- 
ly sinuate  or  a  little  convex.  The  dimensions  of  a  perfect  specimen  are : 
length  of  pedicle  valve  10.9  mm.,  length  of  brachial  valve  9.8  mm.,  greatest 
width  12.7  mm.,  thickness  7.2  mm.,  width  of  sinus  in  front  6.9  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  the  surface  curving  abrupt- 
ly to  the  postero-lateral  margins  and  a  little  inflected  to  the  cardinal 
extremities,  from  the  umbo  to  the  antero-lateral  margins  the  surface  is 
gently  convex  and  from  the  beak  to  the  anterior  margin  along  the 
median  line  it  is  arched  with  the  strongest  curvature  anteriorly;  the 
mesial  sinus  originates  near  the  middle  of  the  valve  and  becomes  rapidly 
deeper  towards  the  front,  where  it  is  a  little  produced  in  a  broadly 
rounded  extension,  its  surface  is  nearly  flat  transversely  in  the  bottom, 
with  the  sides  sloping  outward;  the  beak  is  sharply  pointed  and  only  a 
little  incurved,  being  produced  posteriorly  conspicuously  beyond  the 
incurved  beak  of  the  opposite  valve,  with  its  apex  somewhat  remote  from 
the  umbo  of  the  opposite  valve  ;  the  delthyrium  broadly  triangular,  only  its 
basal  part  filled  by  the  beak  of  the  opposite  valve,  the  remaining  portion 
closed  by  the  deltidial  plates  which  are  sometimes  destroyed  in  the  fossils  ; 
the  plications  simple,  fine  and  subangular  towards  the  beak,  becoming 
acutely  angular  towards  the  front  margin,  four  usually  occupying  the 
sinus,  all  of  which  may  be  included  in  the  bottom  of  the  depression  or  one 
may  be  crowded  up  a  little  way  upon  one  of  the  lateral  surfaces,  from 
eight  to  ten  occupy  each  lateral  slope  of  the  valve,  growing  successively 
smaller  towards  the  cardinal  extremities,  the  last  three  or  four  becoming 
very  faint  and  sometimes  nearly  obsolete ;  the  concentric  markings  of 
the  valve  are  obscure  or  nearly  obsolete,  consisting  of  a  few  faint  lines 
of  growth  which  are  commonly  present  near  the  margin  of  the  valve. 
Internally  the  dental  plates  are  well  developed  and  extend  one-fourth 
or  a  little  more  of  the  length  of  the  valve  anteriorly  from  the  beak. 


L'O'J  Mlssissii'l'lAN    BBACHIOPODA 

Brachial  valve  more  convex  than  the  pedicle,  its  greatest  convexity 
near  or  in  front  of  the  middle,  the  surface  curving  in  nearly  a  quadrant 
of  a  circle  from  the  point  of  greatesl  convexity  to  the  beak,  with  a  much 
gentler  curvature  to  the  anterior  margin;  in  Ilie  umbnnal  region  the 
surface  is  flattened  medially  and  curves  abruptly  to  the  postero-lateral 
margins,  from  the  beak  to  the  antcro  lateral  margins  the  curvature  of 
the  surface  is  nearly  a  semicircle;  the  mesial  fold  originating  in  front  of 
the  middle,  of  only  moderate  beighl  at  the  front  margin ;  the  beak  strongly 
incurved  beneath  that  of  the  opposite  valve;  the  plications  are  similar 
in  form  and  number  to  those  of  the  opposite  valve,  there  being  five  on  the 
mesial  fold  and  from  seven  to  ten  on  each  lateral  slope,  towards  the 
outer  margin  the  plications  are  sharply  angular,  alternating  with  those  of 
the  opposite  valve,  and  giving  to  the  line  of  junction  between  the  two 
valves  a  strongly  zig-zag  direction  along  the  anterior  and  anterolateral 
margins;  concentric  markings  similar  to  those  of  the  opposite  valve. 
Internally  the  binge-plate  is  divided  to  the  apex  of  the  valve  and  is 
entirely  unsupported,  the  cardinal  process,  median  septum,  and  crural 
cavity  wanting. 

Remarks. — This  species  differs  from  A.  heteropsis,  the  genotype,  in  its 
finer  and  more  numerous  plications,  a  larger  number  of  which  occupy  the 
fold  and  sinus,  in  the  more  arched  brachial  valve  from  beak  to  front,  in 
the  less  incurved  beak  of  the  pedicle  valve,  and  usually  in  the  greater 
proportional  width  of  the  shell. 

Locality.— Webb  City,  Mo.  ( ?Carterville  formation). 

Genus  PUGNAX  Hall  and  Clarke 

Description.— Shell  rhynchonelliform,  variable  in  size,  the  mesial  fold 
and  sinus  well  developed,  the  sinus  sometimes  much  produced  in  front, 
the  A'alves  more  or  less  sharply  plicated  with  simple  plications,  those  of 
the  fold  and  sinus  usually  the  stronger  and  all  becoming  obsolete  in  the 
posterior  portion  of  the  shell,  pedicle  valve  shallow  and  brachial  valve 
deep.  Internally  the  hinge-teeth  of  the  pedicle  valve  are  supported  by 
well  developed  dental  lamella?.  In  the  brachial  valve  the  hinge-plate  is 
divided,  the  two  portions  being  unsupported  by  any  lamellae  whatsoever, 
no  median  septum  or  cardinal  process  present. 

^8880 

E  F 

Fig.  13.— A  series  of  six  cross-sections  of  the  rostral  portion  of  the  shell  of 
Pugnax  pugnus  (X  2%),  showing  the  dental  lamellae  of  the  pedicle  valve  and 
the  entire  absence  of  lamellae  in  the  brachial  valve. 


PUGNAX  203 

Remarks.— Several  species  from  our  Mississippian  and  Devonian  faunas, 
which  possess  internal  structures  of  the  rostral  portion  of  the  brachial 
valve  entirely  like  those  of  Camarotcechia  and  not  at  all  agreeing  with 
the  genotype  of  Pugnax,  have  been  referred  commonly  to  the  genus 
Pugnax.  With  the  removal  of  these  species  to  the  new  genus  Pugnoides,  the 
genus  Pugnax  itself  is  left  with  very  meager  representation  in  our  faunas, 
and  of  the  two  species  here  recognized  the  typical  internal  characters 
have  been  observed  in  only  one. 

Pugnax  wortheni  (Hall) 
Plate  XXV,  Figs.  37-42 

1856.     Rhynchonella  Wortheni  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  11. 

1882.  Camarophoria    Wortheni    Whitfield,   Bull.    Am.    Mus.    Nat.    Hist., 

vol.  1,  p.  54,  pi.  6,  figs.  35-39. 

1883.  Camarophoria   (f)   wortheni    Hall,  12th  Rep.  Geol.  Surv.  Tnd.,  p. 

334,    pi.    29,    figs.    35-39. 
1906.     Camarophoria  wortheni    Beede,  30th  Ann.  Rep.  Geol.  Surv.  Tnd., 
p.  1305.  pi.  22,  figs.  35-39. 

Description.  —  Shell  small,  subovate  in  outline,  the  length  and  breadth 
subequal  or  the  width  greater  than  the  length,  the  greatest  width  near 
or  anterior  to  the  mid-length  of  the  shell.  The  dimensions  of  two  indi- 
viduals, the  smaller  one  a  young  example,  are :  length  7  mm.  and  4.5  mm., 
width  7.4  mm.  and  4.5  mm.,  thickness  5.3  mm.  and  2.9  mm. 

Pedicle  valve  gently  convex  in  the  umbonal  region,  flattened  towards 
the  antero-lateral  margins,  and  deeply  sinuate  in  front,  the  edge  of  the 
valve  along  the  postero-lateral  margins  towards  the  beak  is  inflected 
to  form  a  narrow,  pseudo-cardinal  area ;  the  sinus  originates  near  the 
middle  of  the  valve,  is  rapidly  depressed,  and  in  adult  shells  is  produced 
in  front  as  a  linguiform  extension  whose  surface  lies  at  nearly  a  right 
angle  to  the  plane  of  the  valve ;  the  beak  is  pointed,  scarcely  incurved 
and  is  produced  conspicuously  beyond  that  of  the  opposite  valve ;  the 
plications  originate  near  the  middle  of  the  shell,  and  become  rapidly 
stronger  as  they  approach  the  margin,  one  or  two  rounded  ones  occupying 
the  bottom  of  the  sinus  and  about  two,  rarely  more,  more  subangular 
ones  occupying  each  lateral  slope  of  the  valve.  Internally  a  pair  of 
diverging  dental  lamella'  extend  a  short  distance  forward  from  the 
beak. 


<G>  O 


Fig.  14. — A  series  of  two  cross-sections  of  the  rostral  portion  of  the  shell  of 
Pugnax  wortheni  (X  2%),  showing  the  dental  lamellae  of  the  pedicle  valve 
and  the  entire  absence  of  lamellae  in  the  brachial  valve. 


L'04  MISSISSIPPIAN    BRACHIOPODA 

Brachial   valve  more  convex   than  the  pedicle,  becoming  gibbous  in 

front  in  lull  grown  shells,  the  surface  sloping  from  a  point  at  or  near 
the  anterior  margin  with  a  more  or  less  gentle  convexity  to  the  beak, 
t lie  lateral  slopes  of  the  valve  rather  strongly  convex  from  the  beak 
to  the  front;  mesial  fold  strongly  elevated  in  front;  beak  incurved  be- 
neath that  of  the  opposite  valve;  the  plications  similar  to  those  of  the 
opposite  valve,  two  or  three  occupying  the  mesial  fold,  with  about  two 
or  three  upon  each  lateral  slope, 

The  .surface  of  the  shell  marked  by  minute  concentric  lines  of  growth, 
and  in  adull  shells  hv  a  few,  more  or  less  irregular,  stronger  ones  towards 
the   front    margin. 

Remarks.  This  species  was  referred  to  the  genus  Camaroplwria  by 
Whit  field,  and  all  later  writers  have  followed  him  in  this  reference. 
Authentic  specimens,  however,  from  Hull's  Hollow,  above  Alton,  which 
is,  or  is  very  near,  the  typical  locality  for  the  species,  show  that  the 
dental  lamelhe  of  the  pedicle  valve  continue  separately  to  the  bottom 
of  the  valve  and  are  not  united  to  form  a  spondylium  supported  by  a 
median  septum  as  is  true  in  Camarophoria.  Furthermore,  the  rostral 
cavity  of  the  brachial  valve  is  entirely  lacking  in  lamella;  of  any  sort, 
there  being  no  median  septum,  and  no  crural  cavity,  the  internal  charac- 
ters of  both  valves  being  exactly  as  in  typical  representatives  of  the 
genus  Pugnax. 

Horizon.— Salem   limestone. 

Pugnax  quadrirostris  Beede 
Plate  XXV,  Figs.  34-36 

1906.     Pugnax   ?  quadrirostris  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind., 
p.  1306,  pi.  19,  figs.  4-4c. 

Description. — Shell  very  small,  subquadrangular  in  outline,  the  length 
and  breadth  subequal,  the  greatest  width  near  the  middle  of  the  shell. 
The  dimensions  of  a  nearly  perfect  specimen  are :  length  3  mm.,  width  3.4 
mm.,  thickness  2  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  the  surface  curving  ab- 
ruptly from  the  umbonal  region  to  the  postero-lateral  margins,  trans- 
versely between  the  points  of  greatest  lateral  extension  the  surface  is 
nearly  flat,  anteriorly  the  valve  curves  strongly  towards  the  opposite 
valve  and  is  produced  into  a  broad,  elongate,  lingual  extension  whose 
length  in  the  specimen  observed  is  more  than  one-half  the  total  length  of 
the  valve;  mesial  sinus  originating  near  the  beak  as  a  narrow,  rather  ob- 
scure, slightly  impressed  furrow,  anteriorly  it  merges  into  the  broad, 
shallow  mesial  depression  which  extends  nearly  to  the  lateral  extremities 
of  the  valve  and  includes  the  entire  lingual  extension;  beak  short,  a  little 
incurved ;  the  delthyrium  nearly  closed  by  the  beak  of  the  opposite  valve ; 


RHYNCHOTETRA  205 

plications  low  and  obscure,  originating  in  front  of  the  umbonal  region, 
eight  or  ten  may  be  detected  in  the  specimen  studied,  all  of  which  are 
included  within  the  broad  median  sinus,  the  two  median  plications  are  the 
broadest,  the  others  being  much  narrower. 

Brachial  valve  strongly  convex  transversely,  the  surface  along  the 
median  line  describing  a  slightly  sigmoidal  curve,  being  a  little  convex 
posteriorly  and  becoming  slightly  concave  towards  the  front,  from  the 
median  line  the  surface  curves  steeply  to  either  side,  the  least  abrupt 
curvature  being  towards  the  points  of  greatest  lateral  extension  near  the 
mid-length  of  the  valve;  mesial  fold  obscure  posteriorly  but  in  front  of 
the  middle  it  inchides  nearly  the  entire  width  of  the  valve;  beak  small, 
incurved  beneath  that  of  the  opposite  valve  and  nearly  filling  the  delthy- 
rium  of  that  valve ;  plications  obscure,  similar  to  those  of  the  opposite 
valve. 

Surface  of  both  valves  marked  by  exceedingly  fine  concentric  lines  of 
growth. 

Remarks. — Only  a  single  example  of  this  species,  from  Bloomington, 
Indiana,  has  come  under  the  observation  of  the  writer  but  this  specimen  is 
apparently  more  perfect  than  either  of  those  figured  by  Beede.  At  first 
sight  the  shell  seems  to  be  entirely  free  from  plications  but  a  careful  ex- 
amination discloses  them  as  they  have  been  described.  Material  is  not  at 
hand  for  the  investigation  of  the  internal  features  of  the  shell,  but  in  all 
of  its  external  aspects  it  more  closely  resembles  such  typical  members  of 
the  genus  Pugnax  as  P.  aciimiiiatus,  than  any  other  form  which  has  been 
referred  to  that  genus  from  our  Mississippian  faunas.  In  most  respects, 
in  fact,  the  shell  is  only  an  extremely  minute  example  of  P.  acuminatus. 

Horizon.— Salem  limestone. 

Genus  RHYNCHOTETRA  Weller 

Description.— Shells  usually  of  about  medium  size  or  larger,  subovate 
to  triangularly  subovate  in  outline,  often  subcuneate  posteriorly,  the 
valves  subequally  convex  or  the  brachial  valve  more  convex  than  the  ped- 
icle, the  mesial  fold  and  sinus  slightly  developed  or  obsolete.  Both  valves 
marked  by  broad,  rounded  or  subangular  plications  which  are  either 
simple  or  dividing,  and  when  the  surface  is  well  preserved  it  is  also 
marked  by  fine,  radiating  stria? ;  upon  the  postero-lateral  surfaces  of  the 
shell  the  plications  become  obsolete  or  nearly  so.  Internally  the  dental 
Jamelhe  of  the  pedicle  valve  are  strongly  developed,  becoming  joined 
near  the  floor  of  the  valve  to  form  a  broad  and  deep  spondylium  which  is 
supported  by  a  strong  median  septum  and  which  continues  anteriorly 
towards  the  center  of  the  valve.  In  the  rostral  portion  of  the  brachial 
valve  a  strong  median  septum  is  present  which  divides  internally  to  form 
the  walls  of  a  deep  and  rather  narrow  crural  cavity,  posteriorly  the  hinge- 


206 


\l  [SSISSIPPIAN     HKACIIKll'ODA 


plate  is  undivided  so  that  tlie  crural  cavity  is  closed  internally,  but  ante- 
riorly the  hinge-plate  is  divided  and  the  crural  cavity  is  open  as  in 
Camarotccchia,  but  the  borders  of  the  cavity  are  extended  beyond  the 
hinge-plate  and  are  somewhat  convergent  so  that  the  opening  into  the 
crural  cavity  is  narrowed  and  slit-like.  The  crura  are  formed  by  the  an- 
terior extension  of  the  inner  margins  of  the  two  portions  of  the  divided 


Fig.  15. — A  series  of  nine  cross-sections  of  the  rostral  portion  of  the  shell  of 
Rhynchotetra  missouricnsis  (X  2Vz)<  showing  the  dental  lamellae  of  the 
pedicle  valve  joined  to  form  a  spondylium  supported  hy  a  median  septum;  and 
the   median   septum,   crural   cavity,  and   crura  of  the   brachial   valve. 


hinge-plate  and  the  adjacent  portions  of  the  walls  of  the  crural  cavity, 
and  the  median  septum  is  extended  conspicuously  along  the  floor  of  the 
valve  beyond  the  anterior  margin  of  the  crural  cavity. 

Remarks. — The  members  of  this  genus  have  sometimes  been  included  in 
the  pentameroid  genus  Camarophoria  because  of  the  presence  of  a  distinct 
median  septum  in  each  valve,  with  the  spondylium  in  the  pedicle  valve, 
but  they  lack  entirely  the  cruralium  in  the  brachial  valve,  which  is  so 
characteristically  developed  in  that  genus,  between  the  hinge-plate  and 
the  floor  of  the  valve.  Some  of  the  species  have  also  been  described  as 
members  of  the  genus  ParyphorJiynchus  because  of  the  fine  radiating  striae 
upon  the  surface  of  the  shell,  but  the  internal  structure  of  the  two  genera 
is  entirely  different. 

Rhynchotetra  caput-testudinis  (White) 
Plate  XXVII,  Figs.  1-6 

1862.     Rhynchonella  caput-testudmis  White,  Proc.  Boston  Soc.  Nat.  Hist., 

vol.  9,  p.  23. 
1894.     Rhynchonella  sp.   ?  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  pi.  41,  fig.  11. 
1901.     Camarophoria  caput-texturfiiiis  Weller.  Trans.  St.  Louis  Acad.  Sci., 

vol.  11,  p.  196.  pi.  19,  figs.  1-4. 


RHYNCHOTETRA  207 

Description.  —  Shell  above  medium  size,  strongly  plicated,  subtriangu- 
lar  in  outline,  cuneate  posteriorly,  longer  than  wide,  the  greatest  width 
anterior  to  the  middle.  The  dimensions  of  the  most  perfect  of  the  type 
specimens  are:  length  of  pedicle  valve  42  mm.,  length  of  brachial  valve 
40  mm.,  greatest  width  38.6  mm.,  thickness  27  mm.,  width  of  sinus  in  front 
27.3  mm. 

Pedicle  valve  arched  from  the  beak  to  the  front,  the  curvature  becom- 
ing much  more  abrupt  anteriorly,  the  surface  gently  convex  transversely 
in  the  median  portion  of  the  valve,  the  gentle  convexity  extending  to  the 
lateral  margins  in  the  widest  portion,  the  posterolateral  margins  ab- 
ruptly deflected  towards  the  opposite  valve,  the  deflected  portion  on  each 
side  forming  one-half  of  a  flattened  or  concave  oval  region  which  is  pres- 
ent on  each  side  of  the  beak,  and  upon  which  the  plications  are  obscure ; 
mesial  sinus  obscure,  obsolete  in  the  posterior  half  of  the  valve,  becoming 
slightly  depressed  anteriorly  and  produced  in  a  broad  and  rather  long 
lingual  extension ;  beak  small,  pointed,  scarcely  incurved ;  the  plications 
strong,  mostly  simple,  rounded  or  subangular  on  top,  separated  by  broad 
rounded  furrows  of  which  from  16  to  18  are  present  upon  the  valve,  about 
G  or  7  occupying  the  mesial  depression  near  the  front  of  the  valve.  Inter- 
nally the  dental  lamella?  are  well  developed  and  extend  anteriorly  from 
the  baak  for  nearly  one-third  the  length  of  the  valve  with  only  slight  di- 
vergence, they  each  join  the  inner  surface  of  the  valve,  not  being  united 
to  form  a  spondylium  elevated  upon  a  median  septum. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
towards  the  front,  from  this  point  of  greatest  convexity  the  surface 
slopes  to  the  beak  with  a  long,  gentle  convex  curvature,  becoming  a  little 
more  abrupt  near  the  beak,  the  anterior  slope  is  much  shorter,  towards 
the  antero-lateral  margins  the  surface  curves  much  more  abruptly,  and 
towards  the  postero-lateral  margins  it  is  abruptly  deflected  to  meet  the 
similar  deflected  portion  of  the  opposite  valve ;  mesial  fold  ill-defined  and 
obscure,  not  elevated  above  the  general  surface  of  the  valve  in  the  pos- 
terior portion  of  the  valve-  but  more  distinctly  elevated  in  front ;  beak 
pointed  and  incurved  beneath  that  of  the  opposite  valve ;  plications  en- 
tirely similar  to  those  of  the  opposite  valve.  Internally  a  median  septum 
extends  anteriorly  from  the  beak  for  nearly  one-third  the  length  of  the 
valve. 

The  finer  surface  markings  consist  of  minute,  radiating  striae,  and  ex- 
ceedingly fine  concentric  markings,  in  addition  to  which  are  occasional 
stronger,  concentric  lines  of  growth,  the  finer  markings  usually  being 
visable  only  with  a  lens. 

Remarks. — This  species  is  characterized  by  its  nearly  simple  plications 
and  its  rather  broad,  triangularly  subovate  outline.  The  types  of  the 
species  are  three  in  number,  one    nearly    complete    example    with  both 


208  MISSISSII'I'IAN     BRAC 'ODA 

valves  present,  from  a  line  grained,  compact  limestone  which  resembles, 
lithologically,  bed  No.  4  of  the  Kinderhook  at  Burlington,  Iowa.  The 
other  two  examples  are  from  the  porous  brown  limestone  of  bed  No.  7  of 
the  same  section.  In  the  original  description  the  species  is  recorded  from 
"the  base  of  the  Burlington  Limestone."  which,  from  a  consideration  of 
the  specimens,  should  doubtless  be  interpreted  ns  Kinderhook. 

Girty1  has  figured  a  shell  under  the  name  Camarophoria  ringens  which 
is  of  the  type  of  White's  Ehynchonella  cnpnl-testudinis.  This  shell  clearly 
has  the  outline  suggested  by  the  original  definition  of  E.  ringens,  and 
similar  specimens  have  not  infrequently  been  identified  with  Swallow's 
species  by  collectors  in  the  Mississippi  Valley,  although  they  commonly 
possess  a  smaller  number  of  plications  than  Swallow  designates.  This 
type  of  shell  can  scarcely  be  considered  as  representative  of  Swallow's 
species,  however,  because  no  example  of  it  has  ever  been  observed  by  re- 
cent collectors  in  the  cherts  from  which  A',  ringens  is  said  to  have  been 
collected. 

Horizon. — Kinderhook. 

Hiivnchotetra  ovatum  (Greger) 

Plate  XXVII,  Figs.  16-20 

1910.     Paraphorhynchus  ovatum  Greger,    Am.    Jour.    Sci.    (4),    vol.    29, 
p.   74,  figs.  9-10. 

Description.— Shell  of  medium  size  or  somewhat  larger,  subovate  in 
outline,  longer  than  wide,  the  greatest  width  near  the  mid-length,  the 
posterior  extremity  usually  acutely  pointed,  the  line  of  junction  between 
the  valves  deeply  and  strongly  serrate.  The  dimensions  of  a  nearly  per- 
fect specimen,  one  of  the  cotypes,  are :  length  of  pedicle  valve  35.5  mm., 
length  of  brachial  valve  33.3  mm.,  greatest  width  26.8  mm.,  thickness 
18  mm. 

Pedicle  valve  gently  convex  throughout  the  greater  portion  of  its  sur- 
face, its  greatest  depth  near  the  middle,  abruptly  deflected  towards  the 
opposite  valve  near  the  postero-lateral  margins,  the  deflected  surface 
nearly  flat  and  lying  nearly  at  a  right  angle  to  the  plane  of  the  valves 
or  slightly  concave  and  somewhat  inflected  to  the  margin  towards  the 
cardinal  extremities;  mesial  sinus  obscure  or  essentially  obsolete,  when 
best  develoved  it  is  broad,  only  slightly  depressed,  and  restricted  to  the 
extreme  anterior  part  of  the  valve ;  beak  not  prominent,  pointed,  only 
moderately  incurved ;  surface  of  the  valve  marked  by  from  sixteen  to 
twenty,  usually  simple,  strong  but  rather  low,  radiating  plications, 
rounded  on  top  and  separated  by  rounded  furrows,  most  of  them  orig- 
inate near  the  beak,  only  rarely  and  upon  some  specimens  never  do  they 
increase  by  division  or  implantation  upon  the  body  of  the  valve. 

lMon.  U.  S.  Geol.  Survey,  vol.  33,  pt.  2,  pi.  69,  figs,  la-b  (1889). 


K11YNCII0TETRA  209 

Brachial  valve  slightly  deeper  than  the  pedicle  but  similar  in  form, 
it  is  gently  convex  through  the  greater  portion  of  its  surface,  being 
abruptly  deflected  towards  the  opposite  valve  near  the  postero-lateral 
margins,  the  deflected  portion  is  a  little  broader  than  that  of  the  opposite 
valve  and  is  continuous  with  it,  the  two  together  forming  the  subovate, 
flattened  or  slightly  concave  lateral  areas  in  the  posterior  portion  of  the 
shell ;  mesial  fold  obscure  or  obsolete,  when  best  developed  it  is  but 
slightly  differentiated  and  is  restricted  to  the  extreme  anterior  portion 
of  the  valve ;  beak  pointed,  incurved  beneath  that  of  the  opposite  valve ; 
plications  similar  in  all  respects  to  those  of  the  opposite  valve. 

Surface  of  both  valves,  when  well  preserved,  marked  by  flue,  radiating 
stria1,  about  three  or  four  of  which  occupy  the  space  of  one  millimeter. 

L'<  marks. — The  internal  characters  of  this  species  have  not  been  fully 
investigated,  but  the  strong  dental  lamella?  of  the  pedicle  valve  joining 
to  form  a  spondylium-like  cavity  near  the  inner  surface  of  the  valve, 
are  clearly  visible  in  one  example  with  the  rostral  portion  of  that  valve 
broken,  and  in  the  brachial  valve  a  well  developed  median  septum  is 
clearly  seen  upon  the  slightly  weathered  surface.  There  is  no  reason  to 
doubt  but  that  the  arrangement  of  the  internal  lamellae  agrees  essentially 
with  that  of  R.  missouriensis,  which  has  been  carefully  sectioned.  The 
species  agrees  most  closely  with  R.  caput-testudinis,  but  it  is  somewhat 
smaller,  with  much  less  convex  valves,  with  a  more  subovate  outline  and 
somewhat  finer  plications.  It  is  clearly  distinct  from  R.  gibbosum  by 
reason  of  its  less  convex  valves  and  its  simple  plications  which  usually 
originate  near  the  beak  and  continue  to  the  margin  without  additions  by 
subdivision  or  intercalation. 

Horizon.  —  Chouteau    limestone. 


Rhynchotetra  elongatum  n.  sp. 
Plate  XXVIII,  Figs.  9-12 

Description. — Shell  below  medium  size,  longer  than  wide,  the  greatest 
width  in  front  of  the  middle,  the  anterior  portion  of  the  shell  sub- 
semicircular  in  outline,  the  posterior  portion  acutely  subcuneate.  The 
dimensions  of  a  nearly  perfect  individual  are :  length  of  pedicle  valve  27.2 
mm.,  length  of  brachial  valve  26.5  mm.,  width  18  mm.,  thickness  8.5  nun. 

Pedicle  valve  depressed  convex,  greatest  convexity  posterior  to  the 
middle,  nearly  flat  anterior  to  the  middle,  the  postero-lateral  margins 
abruptly  deflected  towards  the  opposite  valve,  the  deflected  portion  on 
each  side  forming  one-half  of  a  suboval,  flattened  or  concave  region 
on  each  side  of  the  beak;  mesial  sinus  essentially  obsolete;  beak  small, 
pointed,  scarcely  incurved;  the  umbonal  region  with  a  median  septum 
internally;  plications  nine  or  ten  in  number,  those  in  the  middle  of  the 


210  MISSISSIPPIAN   BB  \<' 'ni)A 

shell  strong,  becoming  much  fainter  towards  the  postero-lateral  margins, 
mostly  simple,  and  becoming  obsolete  near  the  beak  where  the  nmhonal 
region  for  a  short  distance  is  essentially  nonplicate,  the  plications  are 
subangular  on  top  and  are  separated  by  broad  Farrows. 

Brachial  valve  depressed  convex,  similar  in  form  to  the  pedicle,  the 
surface  gently  arched  from  the  beak  to  the  anterior  and  anterolateral 
margins,  nol  so  much  flattened  anteriorly  as  the  opposite  valve,  the 
postern  lateral  margins  abruptly  deflected  to  meet  the  similar  deflected 
porl  ions  of  the  opposite  valve  and  to  form  a  part  of  the  subovatc  flattened 
regions  on  each  side  of  the  beak;  mesial  fold  obsolete;  beak  small, 
pointed,  incurved  beneath  that  of  the  opposite  valve;  plications  entirely 
similar  to  those  of  the  opposite  valve. 

The  minute  surface  markings  consist  of  extremely  fine,  radiating 
stria-.     Lines  of  growth  of  varying  strength  occur  at  intervals. 

Remarks.  This  shell  is  allied  to  R.  caput-testvdinis,  but  it  differs  from 
thai  species  in  its  much  smaller  size  and  less  convex  valves.  These  char- 
acters might  be  interpreted  as  youthful  characters,  but  the  type  specimen 
has  all  the  appearances  of  being  a  mature  shell.  The  species  also  differs 
from  E.  gibbosum  in  its  smaller  size  and  in  the  absence  of  the  conspicuous 
divarication  of  the  plications.  It  is  perhaps  most  closely  allied  to  F. 
ovatum,  but  it  is  narrower,  much  mlore  elongate,  and  proportionally 
i  banner. 

Horizon.  —  Pierson    limestone    of   the    Kinderhook. 

Rhynchotetra  missouriensis  n.  sp. 
Plate  XXVIII,  Figs.  1-8 

Description. — Shell  of  about  medium  size,  triangularly  subovate  in  out- 
line, longer  than  wide,  the  greatest  width  anterior  to  the  middle,  the 
postero-lateral  margins  nearly  straight  or  a  little  concave,  the  antero- 
lateral margins  rounded,  the  anterior  margin  gently  convex  or  sometimes 
subtruncate.  The  dimensions  of  a  nearly  complete  specimen  are :  length 
of  pedicle  valve  29  mm.,  length  of  brachial  valve  27.5  mm.,  width  27  mm., 
thickness  15.7  mm. 

Pedicle  valve  depressed  convex,  the  surface  gently  and  nearly  regularly 
convex  longitudinally  from  beak  to  front,  and  also  transversely  along 
the  line  of  maximum  width ;  along  the  postero-lateral  margins  the  valve 
is  abruptly  deflected  towards  the  opposite  valve  to  form  a  minor  portion 
of  the  suboval,  flattened  or  somewhat  concave,  lateral  regions  lying  upon 
each  side  of  the  beak;  mesial  sinus  obsolete;  beak  small,  pointed,  only 
slightly  incurved ;  plications  broad,  rounded,  separated  by  rounded  fur- 
rows about  equal  to  the  plications  in  width ;  about  four  or  five  plications 
originate  at  the  beak,  the  two  lateral  ones  each  giving  origin  to  three  or 
four  others  from  their  outer  sides,  the  median  ones  usually  bifurcating 


RHYNCHOTETRA  211 

once  near  or  in  front  of  the  middle,  making  twelve  to  fifteen  plications 
in  all  upon  the  lateral  and  anterior  margins;  internally  the  dental  lamel- 
lae are  strongly  developed  and  are  joined  to  form  a  spondylium  supported 
by  a  median  septum,  as  has  been  shown  in  the  generic  description. 

Brachial  valve  more  convex  and  deeper  than  the  pedicle,  the  greatest 
depth  near  the  middle,  the  surface  curving  from  the  central  point  with 
a  regular  convexity  in  all  directions ;  along  the  postero-lateral  margins 
the  surface  is  abruptly  deflected  towards  the  opposite  valve,  the  deflected 
portion  forming  the  larger  part  of  the  flattened  or  concave  areas  on  each 
side  of  the  beak ;  mesial  fold  obsolete ;  the  beak  small,  pointed,  incurved 
beneath  that  of  the  opposite  valve ;  the  plications  entirely  similar  to  those 
of  the  opposite  valve,  but  with  the  later  ones  added  by  intercalation 
rather  than  by  division.  Internally,  a  median  septum  is  present  which 
is  divided  internally  to  form  a  crural  cavity,  as  has  been  shown  in  the 
generic  description. 

The  minute  surface  markings  consist  of  fine,  radiating  striae.  Lines 
of  growth  of  varying  strength  may  be  present  and  are  sometimes  a  little 
crowded  towards  the  anterior  margin. 

Remarks.— This  species  most  closely  resembles  E.  gibbosum,  but  it  is  a 
much  thinner  species,  with  much  less  convex  valves,  and  with  the  great- 
est width  more  anterior  in  position;  in  the  form  and  arrangement  of  the 
plications,  however,  the  two  species  are  much  alike. 

Horizon. — Burlington  limestone. 

Rhynchotbtra  gibbosum   (Greger) 

Plate  XXVII,  Pigs.  7-15 

1894.     Rhynchonella  sp.  (?)  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  pi.  41,  fig.  8. 
3910.     Paraphorhynchus  gibbosum   Greger,  Am.  Jour.  Sci.   (4),  vol.  29, 
p.   73,   figs.   1-6. 

Description.  —  Shell  strongly  plicate,  of  medium  size  or  larger,  longer 
than  wide,  the  greatest  width  near  or  in  front  of  the  middle,  the  anterior 
outline  usually  subsemicircular,  the  posterior  outline  acutely  subcuneate. 
The  dimensions  of  a  nearly  complete  specimen,  a  cotype,  are :  length 
39  mm.,  width  25.5  mm.,  thickness  28  mm. 

Pedicle  valve  arched  from  the  beak  to  the  front,  but  somewhat  more 
flattened  posteriorly,  arched  to  the  antero-lateral  margins,  the  postero- 
lateral margins  abruptly  deflected  towards  the  opposite  valve,  the  de- 
flected portion  forming  nearly  one-half  of  an  oval,  flattened  or  concave 
lateral  region  upon  each  side  of  the  shell;  mesial  sinus  obsolete  in  the 
posterior  portion  of  the  shell,  broad,  shallow,  obscure  and  ill-defined 
anteriorly ;  beak  small,  pointed,  a  little  incurved ;  plications  strong, 
rounded  on  top,  separated  by  broad,  rounded  furrows,  from  three  to  five 
originate  near  the  beak,  all  or  nearlv  all  of  which  divide  at  intervals 


212  MISSISSIPPI^    BRACHIOPODA 

in  passing  from  the  beak  to  (he  fronl  margin,  the  one  on  each  side  nearest 
to  Hit'  postero-lateral  deflection  of  the  valve  giving  origin  to  four  or 
more  plications  from  its  outer  side  wliieh  are  arched  across  the  oval, 
postero-lateral  flattened  portion  of  the  valve. 

Brachial  valve  more  convex  than  llio  pedicle,  arched  from  the  beak 
to  the  anterior  and  anterolateral  margins,  the  greatest  depth  of  the 
valve  near  the  middle,  the  posterolateral  margins  sharply  deflected 
to  meet  the  similar  deflected  portion  of  the  opposite  valve  and  helping 
to  form  the  oval,  flattened  areas  on  each  side  the  rostral  portion  of  the 
shell;  mesial  fold  obsolete  posteriorly,  obscure  and  poorly  defined  an- 
teriorly; beak  small,  pointed,  incurved  beneath  that  of  the  opposite 
valve;  plications  similar  to  those  of  the  opposite  valve,  but  with  the 
younger  plications  oil  en  added  by  intercalation  instead  of  by  bifurcation  ; 
at  the  postero-lateral  margins  plications  similar  to  those  of  the  opposite 
valve   are   arched   across  the  deflected   portion   of  the  valve. 

The  minute  surface  markings  of  the  shell  consist  of  exceedingly  fine 
radiating  stria'  which  are  crossed  by  fine  concentric  lines  of  growth. 
Stronger  lines  of  growth  are  sometimes  present  at  intervals,  more  es- 
pecially towards  the  anterior  margin. 

Hi  marls.  — In  general  form,  size  and  proportions  this  species  resembles 
ft.  caput-testudinis,  but  it  differs  from  that  species  in  being  notably 
thicker  and  especially  in  the  conspicuous  and  more  or  less  frequent 
bifurcation  or  intercalation  of  plications;  the  presence  of  the  strong 
plications  which  arch  across  the  oval  postero-lateral  regions  of  the  shell 
also   distinguishes   this   species    from   ft.    caput-testudinis. 

Horizon.— Burlington  limestone. 

Genus  TETRACAMERA  Weller 

Description. — Shell  rhynchonelliform,  small  or  of  medium  size,  triangu- 
larly subovate  to  subpentagonal  in  outline,  the  mesial  fold  and  sinus 
poorly  developed  or  nearly  obsolete  except  towards  the  front,  the  lateral 
and  anterior  margins  of  both  valves  deflected  so  as  to  stand  at  nearly 
right  angles  to  the  plane  of  the  valves,  both  valves  marked  by  simple, 
subangular  or  rounded  plications  which  reach  to  the  beak.  Internally 
the  pedicle  valve  possesses  strongly  developed  dental  lamellaa  which 
curve  towards  the  median  line  as  they  approach  the  floor  of  the  valve, 
and  form  a  deep  spondylium  which  rests  upon  the  inner  surface  of  the 
valve  or  is  slightly  raised  on  a  median  septum  anteriorly,  from  the  ex- 
ternal surface  of  each  dental  lamella  a  transverse  buttress  plate  extends 
across  the  intervening  cavity  to  the  inner  surface  of  the  outer  shell  wall. 
In  the  rostral  portion  of  the  brachial  valve  a  strong  median  septum 
is  present  which  is  undivided  at  the  apex  of  the  valve,  but  before  the 
articulation  of  the  shell  is  reached  a  median  incision  is  formed  internally 


TETRACAMEEA 


213 


which  is  at  first  arched  over  but  soon  becomes  open  internally  by  the  in- 
cision between  the  lateral  divisions  of  the  divided  hinge-plate,  the  crural 
cavity  so  formed  being  essentially  identical  with  that  of  Camarotcechia; 
the  cavities  between  the  median  septum  and  the  outer  shell  walls  are 
each  divided  by  a  lamella  or  septum  resting  upon  the  floor  of  the  valve 
and  supporting  the  inner  margin  of  the  corresponding  lateral  division 
of  the  hinge-plate,  these  lateral  septa  extending  farther  anteriorly  than 
the  median  septum. 


Fig.  16. — A  series  of  ten  cross-sections  of  the  rostral  portion  of  the  shell  of 
Tctracamera  subcuncata  (X  2%),  showing  the  dental  lamella?  and  buttress 
plates  of  the  pedicle  valve,  and  the  median  and  two  lateral  lamellae,  the  crural 
cavity  and  crura  of  the  brachial  valve. 

Remarks.— The  species  included  in  this  genus  were  referred  to  Cam- 
arophoria  by  Hall  and  Clarke,1  and  usually  have  been  so  referred  since 
the  publication  of  their  work.  The  shells  do  not  possess  the  character- 
istic cruralium  of  Camiaroplwria,  besides  possessing  other  characters 
wholly  foreign  to  that  genus.  The  most  essential  generic  characters  are 
the  presence  of  the  buttress  plates  connecting  the  dental  lamella?  with 
the  inner  surface  of  the  outer  shell  wall,  and  the  presence  of  the  supple- 
mentary lamella?  in  the  rostral  portion  of  the  brachial  valve  in  addition 
to  the  median  septum.  The  species  T.  subtrigona  which  is  here  included 
in  the  genus  differs  in  a  rather  fundamental  manner  from  the  genotype, 
not  only  in  the  general  form  of  the  shell  but  in  the  arrangement  of  the 
internal  lamella1,  and  should  perhaps  be  made  the  type  of  a  distinct- 
genus,  but  the  discussion  of  these  characters  is  reserved  for  treatment 
under  the  specific  description. 


lPal.  N.  Y.,  vol.  8,  pt.  2,  p.  214  (1894). 


214  m  ississil'l'lAN    BRACHIOPODA 

Tktk  \c\ukk\  SUBCUNEATA  (Hall) 
Plate  XXVI 1 1,  Figs.  13-24 

1856.     Bhynchonella  subcuneata   Hall.  Trans.   Albany  Inst.,  vol.  4,  p.  11. 
1858.     Bhynchonella  subcuneata  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  658, 

pi.  23,  tigs.  3a-c. 
1st;:;.     Bhynchonella  perrostellata   Swallow,  Trans.  St.   Louis  Acad.  Sci., 

vol.  2,  p.  85. 
1882.     h'lnj»c/nni< Ha  subcuneata  Whitf.,   Bull.   Am.  Mus.  Nat.  Hist.,  vol. 

1,  p.  51,  pi.  fi.  figs.  47-4i). 

188:5.    h'hynclioiulhi  subcuneata  Hall.  12th  Rep.  Geol.  Surv.  Ind.,  p.  333, 

pi.  29,   figs.  47-49. 
1894.     Camarophoria   subcuneata    Hall     and    Clarke,    Int.   to   Study   of 

Ui-ach.,    pi.    2,    pi.   45.    figs.   3-4. 

1894.  Bhynchonella  subcuneata  Keyes,  Mo.  (Jeol.  Surv.,  vol.  5,  p.  102. 

1895.  Camarophoria  subcuneata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt. 

2,  pi.  62,  figs.  34-37. 

1906.     Camarophoria  subcuneata  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind., 

p.   1304,  i>l.  22,  figs.  47-49. 
1910.     Tetracamera  subcuneata  Welle!'.  Bull.  Geol.  Soc.  Am.,  vol.  21,  p. 

503,    fig.    4. 

Description.  —  Shell  below  medium  size,  the  valves  subequally  convex, 
subtriangular  in  outline,  usually  broader  than  long,  the  greatest  width 
uear  the  anterior  extremity,  the  long  postero-lateral  margins  straight  or  a 
little  concave,  usually  meeting  at  the  beak  in  an  acute  angle.  The  dimen- 
sions of  two  examples  are:  length  11.7  mm.  and  10.4  mm.,  width  12  mm. 
and  11.5  mm.,  thickness  7.3  mm.  and  6.3  mm.  The  dimension  of  the 
largest  example  observed  are:  length  15.3  mm.,  width  15.3  mm.,  thickness 
9.6  mm. 

Pedicle  valve  depressed-convex,  the  surface  gently  arched  from  the 
beak  to  the  anterior  margin  except  in  old  shells  in  which  the  valve  is 
rather  abruptly  deflected  anteriorly  to  meet  a  similar  deflection  of  the 
opposite  valve,  along  the  postero-lateral  margin  the  valve  is  abruptly 
deflected  towards  the  opposite  valve,  the  deflected  portion  on  each  side 
forming  about  one-half  of  a  smooth,  flattened  or  slightly  concave  region 
on  each  side  of  the  beak ;  mesial  sinus  obsolete  posteriorly  and  repre- 
sented anteriorly  only  as  a  slight,  indefinite  flattening  of  the  valve  which 
sometimes  cannot  be  detected  at  all ;  beak  small,  sharply  pointed,  slightly 
incurved,  the  delthyrium  triangular,  open  towards  the  apex  but  closed 
below  by  the  beak  of  the  opposite  valve ;  plications  angular,  from  12  to 
20  in  number,  either  simple  or  dividing  near  the  beak,  in  no  case  is 
the  bifurcation  upon  the  body  of  the  shell  a  conspicuous  feature. 

Brachial  valve  similar  in  form  to  the  pedicle,  the  surface  arched 
from  the  beak  to  the  anterior  margin,  the  curvature  being  strongest  near 
the  beak,  the  postero-lateral  margins  deflected  to  meet  the  similar  de- 
flected portion  of  the  opposite  valve  and  to  take  part  in  the  formation 


TETRACAMEKA  215 

of  the  flattened  or  concave  lateral  regions  on  each  side  of  the  beak; 
mesial  fold  obsolete ;  beak  strongly  incurved  and  partially  filling  the  del- 
thyrium  of  the  opposite  valve;  plications  entirely  similar  to  those  of  the 
opposite  valve. 

The  minute  surface  markings  consist  of  fine,  obscure,  radiating  stria1 
which  are  usually  obsolete  because  of  the  condition  of  preservation  of 
the  shell  surface,  when  preserved  they  can  be  best  seen  upon  the  flattened, 
postero-lateral  portions  of  the  shell.  Fine  concentric  lines  of  growth 
are  present  when  the  shell  is  properly  preserved,  and  are  subimbricating 
in  character,  stronger  lines  of  growth  occur  at  irregular  intervals.  In 
old  shells  which  are  much  flattened  anteriorly  by  reason  of  the  anterior 
deflection  of  the  valves,  and  to  a  less  extent  in  younger  individuals,  the 
margins  of  the  valves  are  deeply  incised  by  the  interlocking  serrations 
of  the  two  valves,  and  parallel  with  the  line  of  juncture  and  adjacent 
to  it  the  lines  of  growth  are  usually  conspicuously  crowded. 

Eemarks.—This  species  is  a.  highly  characteristic  member  of  the  fauna 
of  the  Salem  limestone.  Its  only  close  ally  is  T.  arctirostrata,  which  is  char- 
acterized by  its  larger  size  and  by  the  presence  of  fine  radiating  stria? 
upon  the  surface  of  the  shell. 

Horizon.  —  Salem    limestone. 

Tetracamera  arctirostrata   (Swallow) 
Plate  XXVIII,  Figs.  25-34 

1863.     lxhynchonella  arctirostrata  Swallow,   Trans.   St.   Louis  Acad.  Sci., 

vol.  2,  p.  84. 
1910.     CamaropJtoria  arctirostrata  Greger,   Am.   Jour.   Sci.    (4),   vol.   29, 

p.  73,  figs.  11-12. 

Description. — Shell  below  medium  size,  length  and  width  sub-equal  or 
somewhat  wider  than  long,  the  greatest  width  in  front  of  the  middle, 
subtriangular  in  outline  with  the  postero-lateral  margins  long  and  nearly 
.straight,  the  antero-lateral  margins  rounded,  the  anterior  margin  some- 
what truncated  or  slightly  convex,  the  line  of  junction  between  the  valves 
deeply  and  sharply  sen-ate.  The  dimensions  of  a  very  perfect  example 
are:  length  of  pedicle  valve  15.6  mm.,  length  of  brachial  valve  14.8  mm., 
greatest  width  15.4  mm.,  thickness  12.8  mm. 

Pedicle  valve  gently  convex  throughout  the  greater  portion  of  its 
surface  and  gently  arched  from  the  beak  to  near  the  front  margin,  to- 
wards the  postero-lateral  margins  the  valve  is  abruptly  deflected  to  the 
margin,  the  deflected  portion  lying  in  nearly  a  right  angle  to  the  plane 
of  the  valve,  antero-laterally  the  deflection  is  only  a  little  less  abrupt 
but  anteriorly  it  is  notably  less,  although  this  margin  also  curves  towards 
the  opposite  valve  until  it  lies  nearly  at  right  angles  to  the  plane  of  the 
valve ;  mesial  sinus  obscure,  sometimes  nearly  obsolete,  when  best  de- 
veloped it  is  broad  and  only  slightly  depressed  and  is  restricted  to  the 


216  MISSISSIPPI  AN    BEACHIOPODA 

anterior  portion  of  the  valve;  beak  acutely  pointed  and  moderately  in- 
curvedj  plications  sixteen  to  twenty  in  number,  simple  and  reaching 
from  the  beak  to  the  margins  without  intercalations,  rounded  posteriorly 
1ml  becoming  more  or  less  sub  angular  near  the  anterior  and  antero- 
lateral margins,  those  upon  the  postero-lateral  deflections  of  the  valve 
curving  strongly  towards  the  margin. 

Brachial  valve  muck  deeper  than  the  pedicle,  its  greatest  depth  near 
the  anterior  margin,  gently  convex  along  the  median  line  from  the  point 
o)'  greatest  depth  to  the  beak  and  curving  abruptly  from  the  same  point 
to  the  anterior  margin,  gently  convex  transversely  across  the  central 
portion  of  the  valve  and  abruptly  deflected  laterally  towards  the  opposite 
valve,  post ero  laterally  the  deflected  portion  is  a  little  concave,  becoming 
a  little  convex  anteriorly,  the  deflected  portion  being  much  broader  than 
the  similar  deflected  portion  of  the  opposite  valve;  mesial  fold  not  dif- 
ferentiated from  the  general  curvature  of  the  valve  except  in  the  sinuosity 
of  the  anterior  line  of  junction  of  the  two  valves;  the  beak  pointed  and 
incurved  beneath  that  of  the  opposite  valve;  plications  similar  in  form 
and  number  to  those  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  tine,  regular,  concentric  lines  of 
growth  which  follow  the  direction  of  the  serrate  margin,  upon  the  older 
portion  of  the  shell  they  are  commonly  obliterated,  even  upon  the  best 
preserved  specimens,  but  towards  the  margin  they  are  clearly  defined 
unless  the  surface  is  exfoliated,  a  few  stronger  lines  of  growth  are  usually 
present  at  irregular  intervals,  or  they  may  be  entirely  absent;  besides 
the  concentric  lines  the  surface  is  marked  by  exceedingly  fine  radiating 
striae  which  are  best  observed  oidy  upon  the  postero-lateral  deflected 
portions  of  the  valves,  and  are  entirely  obliterated  upon  exfoliated  shells. 

Bemarks. — The  internal  characters  of  representative  examples  of  this 
species  have  not  been  carefully  examined  because  of  the  lack  of  material, 
hut  enough  has  been  seen  to  show  that  these  structures  are  essentially 
identical  with  those  of  T.  subcuneata.  Indeed  the  whole  aspect  of  a 
good  example  of  the  species  is  that  of  a  rather  large  specimen  of  T. 
subexmeata,  and  it  is  perhaps  ill-advised  to  consider  these  two  species 
as  distinct.  If  T,  arctirostrata  is  a  good  species  it  must  rest  upon  its 
larger  size,  deeper  brachial  valve,  and  especially  upon  the  fine  radiating 
costae. 

Horizon.— Salem  limestone. 

Tetracamera  missouriensis  n.  sp. 

Plate  XXVIII,  Figs.  35-39 
Description.- — Shell  of  medium  size  or  usually  somewhat  smaller,  trian- 
gularly subovate  in  outline,  the  greatest  width  anterior    to    the  middle, 
usually  longer  than  wide,  the  long  postero-lateral  margins  nearly  straight 


TETRACAMERA  217 

and  meeting  at  the  beak  in  an  acute  angle,  the  anterior  and  antero-lateral 
margins  subsemieircular,  the  line  of  junction  between  the  two  valves 
deeply  and  sharply  serrate,  especially  along  the  anterior  and  antero-lat- 
eral margins.  The  dimensions  of  an  internal  east  of  a  pedicle  valve  are: 
length  22.9  mm.,  greatest  width  20  mm.,  convexity  4.8  mm.  The  dimen- 
sions of  an  internal  cast  of  a  brachial  valve  are :  length  22.7  mm.,  width 
19.4  mm.,  convexity  8  mm. 

Pedicle  valve  nearly  flat  throughout  the  greater  portion  of  its  surface, 
gently  convex  in  the  umbonal  region,  abruptly  deflected  along  its  postero- 
lateral margins  and  only  a  little  less  abruptly  deflected  along  the  anterior 
and  antero-lateral  margins ;  mesial  sinus  essentially  obsolete  or  repre- 
sented only  by  a  slight  sinuosity  of  the  margin  upon  the  anterior  deflected 
portion  of  the  valve ;  beak  acutely  pointed,  only  moderately  incurved ; 
plications  twenty  to  twenty-six  in  number,  rounded  or  subangular,  usually 
simple  and  extending  from  the  beak  to  the  margin,  but  occasionally  with 
one  or  two  intercalated  plications  anterior  to  the  beak,  the  plications  be- 
coming successively  smaller  towards  the  postero  lateral  margins,  those 
upon  the  deflected  postero-lateral  surfaces  of  the  valve  curving  rather 
strongly  towards  the  margin.  Internally  the  dental  plates  are  well  de- 
veloped and  are  joined  near  the  inner  surface  of  the  valve  to  form  a  spon- 
dylium  which  is  supported  by  a  well  defined  median  septum  which  reaches 
anteriorly  about  one-third  the  length  of  the  valve,  from  the  outer  surface 
of  each  dental  lamellae  a  lateral  buttress  plate  passes  to  the  inner  surface 
of  the  postero-lateral  deflected  portion  of  the  valve,  the  buttress  plates 
extending  anteriorly  from  the  beak  for  about  one-third  the  length  of  the 
median  septum. 

Brachial  valve  similar  in  contour  to  the  pedicle,  with  the  postero-lateral 
surfaces  abruptly  deflected  to  meet  the  similarly  deflected  portions  of  the 
opposite  valve,  and  the  anterior  and  antero-lateral  margins  also  deflected 
in  a  manner  similar  to  that  of  the  opposite  valve,  the  non-deflected  sur- 
face of  the  valve  somewhat  more  convex  than  that  of  the  pedicle  valve, 
and  the  depth  of  the  valve  a  little  greater;  mesial  fold  obsolete  except  for 
the  slight  sinuosity  in  the  anterior  margin ;  the  beak  acutely  angular  and 
incurved  beneath  that  of  the  opposite  valve ;  plications  similar  in  form 
and  number  to  those  of  the  pedicle  valve.  Internally  the  median  septum 
extends  anteriorly  from  the  beak  for  from  one-third  to  nearly  one-half 
the  length  of  the  valve,  the  lateral  lamella1  which  support  the  inner  mar- 
gins of  the  divided  hinge-plate  join  the  inner  surface  of  the  valve  at  the 
base  of  the  median  septum  so  that  the  three  lamell*  make  but  a  single 
median  slit  in  the  internal  casts  of  the  valve. 

The  minute  surface  markings  not  preserved  upon  the  internal  casts,  to 
which  observations  were  limited. 


218  MISSISSII'I'IAN    BBACHIOPODA 

li'i  murks. — The  specimens  here  described  occur  commonly  in  the  cherts 
of  Callaway  County,  Missouri,  the  locality  and  horizon  of  the  type  of  the 
species  described  by  Swallow  as  Ehynchonella  ringens,  and  they  conform 
in  general  outline  with  the  shell  suggested  by  the  original  definition  of 
thai  species.  However,  no  examples  have  been  observed  by  the  writer  to 
attain  mole  than  aboul  one-half  the  size  of  Swallow's  type  and  none  of 
the  specimens  exhibit  a  distinct  mesial  sinus,  which,  in  the  original  defini- 
tion of  the  species,  is  said  to  be  broad  and  shallow;  furthermore,  the  plica- 
tions are  more  numerous,  [f  the  shell  here  detined  should  ever  attain  so 
large  a  size  as  is  indicated  by  Swallow,  it  is  not  improbable  that  a  shallow 
mesial  sinus  might  be  developed,  but  the  number  of  plications  ought 
to  be  somewhat  greater  in  the  larger  example  rather  than  smaller.  How- 
ever, it'  Ihis  shell  does  not  belong  to  Swallow's  species,  and  it  is  believed 
thai  it  does  not,  it  must  be  an  undescribed  form. 

The  species  most  closely  resembles  T.  arctirostrata,  but  it  is  a  larger 
and  more  elongate  shell,  and  in  the  specimens  observed,  lacks  a  mesial 
depression  in  the  anterior  portion  of  the  pedicle  valve.  The  species  may 
further  be  differentiated  by  reason  of  the  occasional  intercalation  of 
plications,  in  some  specimens,  which  has  not  been  observed  in 
T.  arctirostrata. 

Locality.  —  Callaway   County,   Missouri    (residual  chert). 

Tetracamera  subtrigona  (Meek  and  Worthen) 
Plate  XXIX,  Figs.  1-13 

1860.     Ehynchonella  subtrigona  Meek  and  Worthen,  Proc.  Acad.  Nat.  Sei. 

Phil.,  p.  451. 
I860.     Ehynchonella  Parvini  McChesney,  Desc.  New  Foss.,  pt.  2,  p.  83. 

1865.  Ehynchonella  Parvini  McChesney,  Plates  111.    New  Spec.  Foss.,  pi. 

6,  figs.  2a-b. 

1866.  Camarophoria  subtrigona  Meek  and  Worthen,  Geol.  Surv.  111.,  vol.  2, 

p.  251,  pi.  18,  figs.'  7a-c. 
1868.     Camarophoria  subtrigona  McChesney,  Trans.  Chicago  Acad.  Sci.,  vol. 

1,  p.  31,  pi.  6,  figs.  2a-b. 
1894.     Camarophoria  subtrigona  Hall  and  Clarke,  Int.  to  Studv  of  Brack., 

pt,  2,  pi.  45,  figs.  1-2. 

1894.  Ehynchonella,  subtrigona  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  102. 

1895.  Camarophoria  subtrigona  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  62,  figs.  38-43. 
1895.     Camarophoria  ringens  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt,  2, 

pi.  84,  fig.  45. 
1910.     Camarophoria  ringens  Greger.  Am.  Jour.  Sci.   (4),  vol.  29,  p.  71, 

figs.  7-8. 
1910.     Tetracamera  subtrigona  Weller.  Bull.  Geol.  Soc.  Am.,  vol.  21,  p. 

504,  fig.  5. 

Description. — Shell  of  medium  size  or  larger,  broadly  subtriangular  or 
subpentagonal  in  outline,  wider  than  long,  truncated  in  front,  with  broad. 


TETEACAMEEA 


219 


simple  plications.  The  dimensions  of  a  nearly  complete  but  somewhat 
distorted  individual  are:  length  32.5  mm.,  width  37  mm.,  thickness  27  mm. 
Pedicle  valve  flattened  on  the  umbo  and  in  front  of  the  umbo,  gently 
convex  from  the  beak  to  the  front  in  the  median  portion,  abruptly  de- 
flected near  the  margin,  the  front  of  the  shell  being  nearly  at  right  angle 
to  the  flattened  umbonal  region,  towards  the  anterolateral  margins  the 
surface  is  at  first  elevated  by  a  gentle  concavity  and  is  then  abruptly  de- 
flected towards  the  opposite  valve  forming  a  sort  of  angular  crest  along 
each  antero-lateral  margin,  the  postero-lateral  margins  are  nearly  straight 
and  meet  at  the  beak  at  an  obtuse  angle  of  about  110  degrees,  along  these 
margins  the  surface  is  abruptly  bent  towards  the  opposite  valve,  and  is 
usually  somewhat  inflected  forming  with  a  similar  area  on  the  opposite 
valve,  an  obscurely  plicated,  flattened  or  concave  area  on  each  side  of  the 
beak ;  mesial  sinus  broad,  shallow,  ill-defined,  becoming  somewhat  deeper 
anteriorly ;  the  beak  small,  pointed  and  moderately  incurved ;  the  plica- 
tions are  strong,  simple,  rounded  or  a  little  subangular,  and  are  separated 
by  more  angular  furrows,  from  14  to  20  are  present  on  the  valve,  several 


Fig.  17. — A  series  of  sixteen  cross-sections  of  the  rostral  portion  of  the  shell  of 
Tetracamcra  suMrigona  (X  l1^).  showing  the  characters  of  the  internal 
lamellae. 


next  the  postero-lateral  margins  often  being  faint  or  nearly  obsolete, 
about  six  or  seven  occupy  the  mesial  sinus,  the  margin  of  the  valve  is 
deeply  and  acutely  serrate,  the  projections  being  opposite  the  furrows 
between  the  plications,  the  deepest  and  strongest  serrations  are  in  the 
front  of  the  shell,  on  each  side  they  decrease  in  strength  with  the  weaken- 
ing of  the  plications.  Internally  a  strong  median  septum  extends  from 
the  beak  nearly    to    the   line  of   deflection  of  the   valve  near  its  anterior 


220  \i  ississiiti an    BRACHIOPODA 

margin  and  is  often  more  or  less  abruptly  thickened  near  its  anterior  ex- 
tremity, this  septum  supports  a  spondylium  whose  spreading  sides  meet 
;it  an  angle  in  the  bottom. 

Brachial  valve  much  deeper  than  the  pedicle,  the  greatest  depth  near 
the  front  margin;  from  this  point  the  surface  slopes  with  a 
gentle  convex  curvature  to  the  beak,  and  is  abruptly  deflected  to 
the  anterior  and  antero-lateral  margins,  along  the  posterolateral  margins 
the  surface  is  abruptly  benl  towards  the  opposite  valve  and  is  usually 
somewhat  inflected  and  forms  more  than  one-half  of  the  smoolh,  oval, 
concave  areas  on  each  side  of  the  beak;  mesial  fold  obsolete  posteriorly, 
broad  and  ill-defined  anteriorly;  the  beak  is  strongly  incurved  beneath 
that  of  the  opposite  valve  and  partly  Mils  the  delthyrium  of  that  valve, 
the  plications  are  similar  to  those  of  the  opposite  valve  and  are  alternate 
with  them,  as  are  the  serrations  on  the  margin,  the  plications  towards  the 
postero-lateral  margins  are  strongly  arched.  Internally  the  valve  bears 
a  strong  median  septum  which  extends  from  the  beak  more  than  half  way 
to  the  line  of  deflection  of  the  valve  towards  its  anterior  margin,  in  its 
anterior  half  this  median  septum  bisects  a  subovate  or  subelliptical  mus- 
cular impression,  at  the  beak  of  the  valve  it  supports  a  subquadrangular, 
spoon-shaped  hinge-plate  whose  ventral  surface  is  depressed  medially 
through  about  one-third  its  width,  the  lateral  margins  of  this  depressed 
region  diverge  from  a  point  at  the  beak  and  are  overhanging  so  as  to  give 
to  the  depressed  region  the  appearance  of  a  flattened,  conical  tube  cleft 
along  one  side. 

In  addition  to  the  plications  each  valve  is  marked  only  by  concentric 
lines  of  growth  which  are  obscure  or  obsolete  over  the  greater  portion  of 
the  shell,  ordinarily  being  clearly  recognizable  only  upon  the  deflected 
portion  of  the  valves  near  the  anterior  margin. 

Remarks. — This  species  has  been  most  commonly  recognized  in  the  re- 
sidual cherts  of  the  Keokuk  limestone,  where  it  occurs  in  the  condition  of 
internal  casts  showing  clearly  the  median  septum  in  each  valve  and  the 
muscular  impressions  of  the  brachial  valve.  Where  it  has  been  found 
in  sihi  it  is  known  only  in  the  Keokuk  limestone.  Hall  and  Clarke1  have 
illustrated  an  internal  cast  under  the  name  Camarophoria  ringens  Swallow, 
which  is  clearly  an  example  of  Meek  and  Worthen's  Bhynchonella  sab- 
trigona,  and  more  recently  a  specimen  of  the  same  species  has  been  figured 
by  Greger2  as  typical  of  Swallow's  species.  Swallow's  type  has  been  de- 
stroyed but  the  specimen  illustrated  by  Greger  is  said  to  bear  a  label  writ- 
ten by  Swallow  himself  and  is  therefore  considered  by  that  writer  to  be 
authentic,  a  conclusion  which,  if  true,  would  necessitate  Swallow's  name 
taking  precedence  over  that  of  Meek  and  Worthen.     A  careful  examina- 

1  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  84,  fig.  45.     (1895.) 

2  Am.  Jour.  Sci.  (4),  vol.  29,  p.  71.  figs.  7-8.     (1910.) 


SHUMARDELLA  221 

Hon  of  a  score  or  more  of  good  examples  of  Meek  and  Worthen's  species, 
in  comparison  with  Swallow's  original  definition  of  B.  ringens,  brings  out 
the  fact  that  they  are  always  very  different  in  outline  from  the  shell  in- 
dicated by  Swallow.  B.  sitbtrigona  is  always  notably  broader  than  long, 
while  B.  riiuji  us  is  distinctly  defined  as  being  longer  than  broad.  The 
species  is  a  close  ally  of  the  rare  B.  isorhynclia  M'Coy,  from  the  Mountain 
Limestone  fauna  of  Ireland,  but  the  American  species  is  much  broader 
than  the  Irish  form  with  more  conspicuously  deflected  anterior  and  antero- 
lateral margins.  The  crest-like  elevation  of  the  antero-lateral  margins 
of  the  pedicle  valve  of  C.  subtrigona  is  also  lacking  in  C.  isorhynclm. 

The  internal  characters  of  this  shell  differ  somewhat  notably  from  those 
of  the  genotype  of  Tctracamera.  The  characteristic  buttress  plates  are 
present  in  the  pedicle  valve,  but  the  arrangement  of  the  lamella;  in  the 
rostral  portion  of  the  brachial  valve  is  quite  different.  These  differences 
may  be  best  comprehended  through  a  comparison  of  the  sections  which 
are  given  of  the  two  species.  It  is  possible  that  this  species  should 
properly  be  recognized  as  a  member  of  a  distinct  genus,  but  for  the 
present  it  seems  best  to  consider  it  as  congeneric  with  T.  subcuneata. 

Horizon. — Keokuk  limestone. 

Genus  SHUMARDELLA  Weller 

Description. — Shell  rhynchonelliform,  usually  below  medium  size,  sub- 
ovate  to  subpentagonal  in  outline,  often  subglobular  in  form,  the  mesial 
fold  and  sinus  well  developed  anteriorly,  the  anterior  margin  of  the  sinus 
much  produced ;  the  surface  marked  by  broad,  low,  rounded  or  subangii- 
lar  plications  which  are  more  strongly  defined  on  the  fold  and  sinus,  and 
which  may  be  nearly  obsolete.  Internally  the  dental  lamella?  of  the 
pedicle  valve  are  well  developed.  In  the  brachial  valve  a  strong  median 
septum  is  present  and  is  divided  internally  to  form  a  narrow  and  deep 
crural  cavity  which  is  closed  on  its  cardinal  side,  this  closure  being  con- 
tinuous to  beyond  the  point  where  the  median  septum  is  joined  to  the 
hinge-plate,  the  lateral  walls  of  the  crural  cavity  being  suspended  in 
the  cavity  of  the  valve  for  a  short  distance  beyond  the  point  where  they 
are  connected  with  the  median  septum.  The  crura  are  formed  by  the  an- 
terior extension  of  the  walls  of  the  crural  cavity  where  they  are  joined  to 
the  hinge-plate. 

Remarks. — This  genus  is  characterized  by  the  obsolescent  plications  of 
the  shell  and  by  the  crural  cavity  which  is  short  in  an  antero-posterior 
direction  and  entirely  closed  on  its  cardinal  side. 


1855. 

1894. 
1910. 


\i  ississhtian    BRACHIOPODA 
Sin   WAHDELLA  MISSOUBIENSIS   (Shumard) 

Plate  XXV,  Figs  4:5-52 

Rhynckonella  Missouriensis  Shumard,  Geol.  Rep.  Mo.,  p.  204,  pi.  C, 

figs.  5a-c. 
Ehynchonella  missouriensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  100. 
Shumardella   missouriensis   YVeller,    Hull,   Geol.   Soc.   Am.,  vol.  21, 

p.  512.  fig.  14. 

Description,  -Shell  below  medium  .size,  triangularly  subovate  in  outline, 
usually  wider  than  long,  the  greatest  width  anterior  to  the  mid-length, 
the  postero-lateral  margins  nearly  straight,  meeting  at  the  beak  in  an 
angle  of  about  100  degrees,  the  antero-lateral  margins  rounded,  the  an- 
terior margin  nearly  straight  or  slightly  emarginate.  The  dimensions 
of  two  nearly  perfect  specimens  are:  length  20  mm.  and  18  mm.,  width 
22.4  nini.  and  17.9  mm.,  thickness  16.5  mm.  and  15  mm.,  width  of  sinus  in 
front  16  mm.  ami  14. S  mm. 

Pedicle  valve  very  shallow,  the  umbo  narrowly  convex,  usually  with  a 
small  concave  region  on  either  side,  beyond  which  a  narrow  margin,  be- 
coming abruptly  wider  towards  the  beak,  is  sharply  inflected,  towards  the 
antero-lateral  margins  the  surface  is  nearly  flat  or  slightly  convex,  and 
from  the  beak  to  the  front  along  the  median  line  it  is  strongly  but  not 
regularly  arched;  the  mesial  sinus  originates  posterior  to  the  middle  of 
the  valve,  it  is  broad  and  of  moderate  depth  with  the  surface  rather  ab- 


8888 

F  G  H  I 

Fig.  18. — A  series  of  nine  cross-sections  of  the  rostral  portion  of  the  shell  of 
Shumardella  missouriensis  (X  2%),  showing  the  dental  lamellae  of  the  pedicle 
valve,  the  hinge-plate,  median  septum,  crural  cavity,  and  crura  of  the 
brachial  valve. 

ruptly  curved  towards  the  opposite  valve  anteriorly  and  produced  into  a 
broad,  lingual  extension  at  nearly  a  right  angle  to  the  plane  of  the  valve, 
it  is  coarsely  serrate  on  the  front  margin ;  beak  small,  pointed,  moderately 
incurved;  the  delthyrium  nearly  filled  by  the  beak  of  the  opposite  valve. 


SHUMARDELLA  223 

the  deltidial  plates  not  observed;  plications  few  in  number,  broad,  low, 
rounded,  two,  or  more  rarely  three,  originating  on  or  just  in  front  of  the 
umbonal  region  and  occupy  the  bottom  of  the  sinus,  on  each  lateral  slope 
of  the  valve  two  plications  are  usually  present  which  are  fainter  than 
those  of  the  sinus  and  originate  closer  to  the  margin.  Internally  the  teeth 
are  supported  by  a  pair  of  dental  plates  which  quickly  become  obsolete 
in  front  of  the  articulation  of  the  hinge. 

Brachial  valve  gibbous,  the  greatest  depth  near  the  front  margin  in 
adult  examples,  the  surface  usually  slopes  along  the  median  line  from  the 
point  of  greatest  convexity  to  the  beak  with  a  nearly  regular  curvature, 
becoming  a  little  more  convex  near  the  beak,  anteriorly  there  is  often  a 
short  but  somewhat  abrupt  slope  to  the  margin,  towards  the  lateral  mar- 
gins the  surface  curves  at  first  gently  and  then  more  abruptly  from  the 
median  line,  and  towards  the  beak  on  either  side  there  is  a  distinct  and 
sometimes  rather  deep  lateral  concave  region;  mesial  fold  scarcely  or  not 
at  all  differentiated  in  the  posterior  half  of  the  valve,  usually  becoming 
more  prominent  anteriorly ;  beak  incurved  beneath  that  of  the  opposite 
valve ;  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve,  the  three  or  rarely  four  of  the  mesial  fold  alternate  with  those  of 
the  sinus  and  are  the  strongest  ones  on  the  valves,  those  of  the  lateral 
slopes  often  nearly  or  quite  obsolete.  Internally  there  is  no  cardinal  pro- 
cess, a  thin  and  rather  short  median  septum  is  present  supporting  the  in- 
itial portion  of  the  hinge-plate,  at  the  apex  of  the  beak  this  septum  is  not 
divided  but  anteriorly  it  is  split  into  two  parts,  one  of  which  supports 
each  side  of  the  hinge-plate,  but  the  base  of  the  hinge-plate  is  solid  and 
roofs  over  the  cavity  between  the  two  divisions  of  the  septa,  so  that  they 
do  not  form  an  open  crural  cavity  such  as  is  present  in  the  genus 
Camarotcechia,  anteriorly  the  hinge-plate  is  divided  and  at  the  point  of 
articulation  of  the  hinge  the  two  divisions  are  separate  and  the  median 
septum  is  so  much  reduced  that  it  no  longer  supports  them.  The  crura  ex- 
tend from  the  anterior  extremities  of  the  divided  hinge-plate  into  the 
cavity  of  the  shell. 

The  surface  of  both  valves  is  marked  by  fine,  regular,  concentric  striae, 
and  usually  by  several  stronger,  irregularly  developed,  concentric  lines  of 
growth  towards  the  front. 

Hi  marks. — This  species  has  been  frequently  misinterpreted.  Every 
published  illustration  to  which  the  name  has  been  applied,  save  only  the 
original  one  by  Shumard,  is  incorrectly  identified,  and  even  this  author 
lias  represented  two. different  species.  The  name  missouriensis  is  here  re- 
tained for  the  larger  form  illustrated  by  Shumard,  and  the  one  with 
which  his  description  more  fully  agrees.  The  species  is  restricted  to  the 
Chouteau  limestone  fauna  and  is  most  commonly  represented  in  the  typi- 
cal Chouteau  limestone  in  central  Missouri. 


L'L'4  MISSISSIPPIAN    BRACHIOPODA 

The  later  authors  who  have  referred  to  the  species  have  placed  it  in  the 
genus  Vugnax,  bu1  the  distinct  median  septum  of  the  brachial  valve,  which 
is  divided  above  for  the  support  of  the  binge-plate  is  entirely  different  from 
those  characters  in  Pugnax.    It.  differs  i'rom  Camarotcechia  in  the  arching 

over  of  the  Cavity  between  the  divisions  of  the  median  septum  by  the  iiii- 
di\  ided  basal  portion  of  the  hinge-plate,  and  by  the  consequent  absence  of 
the  open  crural  cavity  at  the  base  of  tlie  hinge-plate.  These  internal  char- 
acters, as  well  as  the  external  aspect  of  the  shell,  distinguish  the  species 
from  any  of  the  recognized  generic  divisions  of  rhynchonelloid  shells  and 
it  is  iu  consequence  made  the  type  of  a  new  genus. 
Horizon. — Chouteau  limestone. 

Shumardella  obsolens   (Hall) 
Plate  XXVI,  Figs.  1-9 

1855.     Bhynchonella  obscura-pUcata  Shumard,  I  and  II,  Rep.  Geol.  Surv. 

Mo.,  p.  L'bs.     (Name  only.) 
1855.     Bhynchonella   Missouriensis  Shumard,  I  and  II  Rep.   Geol.  Surv. 

Mo.,  p.   204,  pi.  C,  fig.  5a   (not  figs.  5b-c). 
1860.    Bhynchonella  {Eatonia)  obsolens  Hall,  13th  Rep.  N.  Y.  State  Cab. 

Nat.  Hist.,  p.  111. 
1866.    Bhynchonella   missouriensis  Meek  and  "VVorthen,  Geol.  Surv.  111., 

vol.  2,  p.   153,   pi.   14.  figs.  4a-b. 
1910.     Shumardella   ohsolescens   Weller,   Bull.    Geol.    Soc.   Am.,    vol.    21, 

p.  513,  fig.  15. 

Description. — Shell  below  medium  size,  nearly  smooth,  subglobular  in 
form,  wider  than  long,  the  greatest  width  near  the  mid-length,  posterior 
lateral  margins  meeting  at  the  beak  in  an  obtuse  angle,  the  lateral  mar- 
gins rounded,  the  anterior  margin  emarginate.  The  dimensions  of  two 
perfect  specimens  are :  length  15.9  mm.  and  14.4  mm.,  width  16.7  mm. 
and  16.4  mm.,  thickness  13.7  mm.  and  12.8  mm.,  width  of  sinus  in  front 
11  mm.  and  9.5  mm. 

Pedicle  valve  shallow,  convex  on  the  umbo,  the  surface  gently  convex 
from  the  umbo  to  the  antero-lateral  margins,  curving  strongly  to  the 
postero-lateral  margins,  the  curvature  becoming  more  abrupt  towards  the 
beak,  from  the  beak  to  the  front  margin  along  the  median  line  the 
curvature  of  the  surface  is  a  subsemicircle ;  mesial  sinus  obsolete  in  the 
umbonal  region,  originating  as  a  broad,  shallow,  rounded  depression  post- 
erior to  the  middle  of  the  shell  and  becoming  rapidly  deeper  anteriorly, 
in  front  it  is  produced  in  a  broad,  elongate,  terminally  rounded  lingual 
extension  which  retains  its  concavity  to  the  end  giving  to  the  shell  its 
emarginate  outline  in  front ;  beak  small,  incurved,  nearly  in  contact  with 
the  umbo  of  the  opposite  valve ;  the  delthyrium  nearly  filled  by  the  beak 
of  the  opposite  valve,  the  deltidial  plates  obscure  and  not  observed  in 
any  of  the  specimens  studied,  the  foramen  small ;  plications  nearly  obso- 


SHUMABDEUjA 


225 


lete,  from  two  to  live,  more  usually  two  or  three,  originate  on  or  in  front 
of  the  umbonal  region  and  pass  to  the  anterior  margin  along  the  bottom 
of  the  sinus,  these  plications  are  low  and  rounded,  somewhat  variable 
in  strength   but  always  comparatively  faint,  upon    the    lateral    slopes    of 


0 


Fig.   19. — A  series  of  eight  cross-sections  of  the   rostral  portion  of  the   shell   of 
Shumardrlla  obsolens   (X    2%),  showing  the  internal  characters. 


the  valve  the  plications  are  obsolete.  Internally  the  hinge-teeth  are 
supported  by  short  dental  plates  which  scarcely  extend  beyond  the  articu- 
lation of  the  hinge. 

Brachial  valve  gibbons,  the  umbonal  region  protuberant,  sometimes 
extending  nearly  as  far  as  the  beak  of  the  opposite  valve,  the  greatest 
convexity  near  the  anterior  margin,  the  surface  strongly  convex  from 
beak  to  front  along  the  median  line,  and  much  more  strongly  convex 
transversely,  towards  the  beak  the  surface  on  each  side  is  a  little  in- 
flected to  form,  with  a  similar  inflected  portion  of  the  opposite  valve,  a 
small,  more  or  less  conspicuous  concave  lateral  region ;  mesial  fold  obscure 
or  obsolete  in  the  posterior  half  of  the  valve,  becoming  a  little  more  con- 
spicuous anteriorly,  but  rarely  or  never  strongly  differentiated  from  the 
general  surface  of  the  valve ;  the  beak  incurved  beneath  that  of  the 
opposite  valve;  plications  obscure  as  in  the  opposite  valve,  the  stronger 
ones  are  confined  to  the  mesial  fold  where  they  alternate  with  those  of 
the  sinus  of  the  opposite  valve,  upon  each  lateral  slope  two  or  three 
exceedingly  faint  plications  may  occasionally  be  detected,  but  they  are 
more  apt  to  be  entirely  obsolete.  Internally  there  is  no  cardinal  process ; 
the  binge-plate  is  divided  but  not  to  the  base  at  the  apex  of  the  valve, 
it  is  supported  posteriorly  by  a  median  septum  which  is  simple  at  first 
hut  is  divided  above  anteriorly,  each  division  supporting  one  side  of  the 
hinge-plate,  the  support  of  the  hinge-plate  by  the  divided  septum  does 
not  continue  beyond  the  median  incision  of  the  hinge-plate  itself  so  that 
no    open    crural    cavity    occurs,    but    rather  an    enclosed  cavity    roofed 


226  MISSlssiri'lAN    BRACHIOPODA 

over  by  the  joined  portion  of  the  hinge-plate  and  open  only  in  an  anterior 
direction,  the  support  of  the  hinge-plate  by  the  septum  is  discontinued 
before  the  Line  of  articulation  is  reached  anfl  from  this  point  forward 
each  Lateral  division  of  the  hinge-plate  is  unsupported,  anteriorly  each 
division  is  produced  into  the  cavity  of  the  valve  as  one  of  the  crura 

Surface  of  l»olh  valves  marked  by  fine,  rather  regular  concentric 
striae  and  by  occasional  strong  lines  of  growth. 

Remarks. — Shumard  illustrated  two  different  individuals  with  his 
original  description  of  Rhynchonella  missouriensis,  fig.  5a  being  a  smaller 
and  much  smoother  shell  than  figures  .r)l)-c  The  original  description  was 
evidently  made  from  the  Larger  and  more  Strongly  plicated  shell,  and 
that  is  here  taken  as  the  typical  form  of  the  species.  Both  of  the  illus- 
trated  forms  are  commonly  represented  in  collections  of  the  Chouteau 
Limestone  fauna  from  central  Missouri,  and  while  an  imperfect  gradation 
from  one  form  to  the  other  can  be  traced,  the  two  forms  are  easily  distinct 
enough  to  he  considered  as  different  species.  In  his  lists  of  species 
Shumard  records  //.  obscuro-plicata,  a  name  by  which  he  undoubtedly 
designated  the  shell  here  described,  although  he  never  defined  it.  and 
the  name  by  which  Missouri  collectors  have  known  it  since  that  time. 
In  1860  Hall  described  Rhynchonella  obsolens,  without  illustrations,  from 
the  goniatite-bearing  Rockford  limestone  of  Indiana,  and  his  description 
agrees  fairly  well  with  examples  of  this  smooth  form  from  the  Chouteau 
limestone  of  Missouri.  Tn  1866  Meek  and  Worthen  described  and  illus- 
trated as  7?.  missouriensis  a  shell  from  the  same  Rockford  limestone  which 
agrees  satisfactorily  with  the  smooth  form  of  that  shell  as  illustrated  by 
Shumard,  and  it  is  more  than  probable  that  the  observers  had  rep- 
resentatives of  the  same  shell  as  that  described  by  Hall.  Under  these 
circumstances,  therefore,  if  we  restrict  the  use  of  the  name  missouriensis 
to  the  larger  shell  of  Shumard,  either  Hall's  name  or  Shumard 's  obscuro- 
plicata  may  be  available  for  the  form  here  described,  and  the  latter  of 
these  must  be  ruled  out  because  it  was  never  properly  defined. 

In  their  generic  characters,  as  shown  by  serial  sectioning  of  the  shells, 
h'.  missouriensis  and  R.  obsolens  are  identical,  but  they  cannot  be  included 
in  any  of  the  recognized  generic  divisions  of  rhychonelloid  shells  and  have 
been  made  to  constitute  the  new  genus  Shumardella.  S.  obsolens  may  be 
distinguished  from  8.  misscttrit  nsis  by  its  smaller  size,  its  more  globose 
and  less  angular  form,  its  much  smoother  and  less  strongly  plicated 
shell,  and  by  the  more  distinctly  emarginate  anterior  outline. 

The  species  has  some  external  resemblance  to  members  of  the  genus 
Liorhynchus  and  has  sometimes  been  incorrectly  identified  as  L.  boonen- 
sis,  a  rare  species  which  was  originally  described  from  the  Burlington 
limestone. 

Horizon.  —  Chouteau    limestone. 


R&YNCHOPORA  221 

Genus  RHYNCHOPORA  King 

Description. — Shell  rhyncholliform,  below  medium  size,  usually  pentan- 
gularly  ovate  in  outline,  the  mesial  fold  and  sinus  well  developed  in  the 
anterior  half  ol'  the  shell,  both  valves  marked  by  simple,  subangular  or 
rounded  plications  which  are  sometimes  longitudinally  grooved  towards 
the  front.  Internally  the  dental  lamella'  are  well  developed  in  the  pedicle 
valve.  Brachial  valve  with  a  strong  median  septum  in  the  rostral  por- 
tion, which  is  divided  internally  to  form  the  walls  of  a  crural  cavity ;  this 
is  covered  over  on  its  cardinal  side  by  the  undivided  hinge-plate,  the 
hinge-plate  continuing  anteriorly  beyond  the  anterior  termination  of  the 
crural  cavity ;  the  crura  formed  by  the  anterior  extension  of  that  part 
of  the  hinge-plate  opposite  the  lateral  walls  of  the  crural  cavity.  .Shell 
structure  punctate. 

Remarks.— Ho  opportunity  has  been  afforded  the  writer  to  make  a 
study  of  the  internal  characters  of  R.  geinitziana,  the  genotype  of  Rhyn- 
chopora,  so  there  is  a  possibility  of  a  wrong  interpretation  of  the  genus 
in  this  place.  Up  to  the  present  time  the  one  essential  generic  character 
which  has  been  recognized  is  the  punctate  structure  of  the  shell,  but  in 
E.  pustulosa,  the  only  American  species  recognized  by  Hall  and  Clarke1 
and  by  Schuchert;-  the  undivided  hinge-plate  and  the  complete  closure 
of  the  crural  cavity  except  anteriorly,  are  good  differential  characters. 
All  other  species  included  in  the  genus  in  this  place,  except  one,  agree  in 
the  character  of  the  hinge-plate  and  crural  cavity  with  R.  pustulosa. 
The  puncate  structure  of  the  shell  is  conspicuously  developed  in  only 
one  of  the  species  here  recorded,  R.  beecheri,  which  has  been  observed  only 
in  the  condition  of  internal  casts  and  impressions  of  the  exterior,  no 
serial  sections  of  the  rostral  portion  of  the  shell  have  been  made,  but  the 
hinge-plate  and  crural  cavity  are  apparently  as  in  R.  pustulosa.  The 
Pennsylvanian  species  R.  illinoisensis  is  another  one  which  is  conspicuously 
punctate,  but  its  internal  characters  have  not  been  worked  out.  In  R. 
pustulosa  the  punctate  structure  of  the  shell  is  so  obscure  as  to  almost 
lead  one  to  believe,  at  times,  that  it  is  absent,  and  in  one  or  two  of  the 
species  here  included  in  the  genus  no  punctate  structure  has  yet  been 
observed.  Another  character  which  differentiates  most  of  these  shells 
from  other  Mississippian  rhynchonelloids  is  the  longitudinal  grooving  of 
the  flattened  plications  towards  the  front,  especially  those  of  the  fold 
and  sinus,  this  condition  being  altogether  similar  to  that  in  Wilsonia 
and  some  other  older  rhynchonelloids.  This  character  is  not  shown  upon 
any  of  the  illustrations  of  />'.  geinitziana  which  have  been  available  for 
examination,  and  it  is  not  present  in  R.  hamburgensis  described  in  this 
work.     On  the  whole,  R.  haniburg&^sis  seems  to  correspond  most  closely 

i  Pal.  N.  Y.,  vol.  8,  pt.  2,  p.  210.     (1894.) 
i' Synop.  Am.  Foss.  Brach.,  p.  366.     (1897.) 


228  M  ississi I'lM  \ X    BRACHIOPODA 

in  the  sum  of  all  its  characters,  with  the  genotype,  although  the  punctate 
structure  is  much  more  obscure.  It  is  possible  that  Euture  investigations 
of  Ibis  group  ol'  sbells  will  make  il  necessary  to  recognize  one  or  more 
additional  genera. 

Rhynchopora  hamburgensis  Weller 
Plate  XXIX,  Figs.  19-30 

l!Hii.     Rhynchopora  hamburgensis  Weller.  Bull.  Geol.  Soc.  Am.,  vol.  21, 
p.   515,   fig.    17. 

Description. — Shell  small  with  valves  very  unequally  convex  in  mature 
specimens,  triangularly  subovate  in  outline,  the  posterolateral  margins 
meeting  at  the  beak  in  an  obtuse  angle,  the  antero-lateral  margins 
rounded,  the  anterior  margin  nearly  straight  or  a  little  concave.  The 
dimensions  of  two  examples  are:  Length  10.2  mm.  and  !)  mm.,  width 
11.1  mm.  and  9.8  nun.,  thickness  S  mm.  and  5.5  mm.,  width  of  sinus  in 
front  S  nun.  and  (>.:i  mm. 

Pedicle  valve  shallow,  convex  in  tbe  umbonal  region,  the  surface  curv- 
ing rather  abruptly  to  the  postero-lateral  margins,  gently  convex  from 
the  umbo  to  the  antero-lateral  margins,  and  strongly  arched  in  adult 
shells  along  the  median  line  from  the  beak  to  the  front  margin;  mesial 
sinus  originating  near  the  middle  of  the  valve  as  a  broad,  shallow,  concave 
depression  which  becomes  deeper  anteriorly,  not  abruptly  depressed  below 
the  lateral  slopes  of  the  valve,  produced  anteriorly  in  adult  shells  in  a 
broad  lingual  extension  rounded  in  front,  whose  surface  lies  in  nearly 
a  right  angle  to  the  plane  of  the  valve;  beak  rather  broad,  not  strongly 
incurved,  pierced  by  a  subcircular  foramen,  rather  conspicuously  ex- 
tended posteriorly  beyond  the  opposite  valve;  delthyrium  broadly  triangu- 
lar, partially  filled  by  the  beak  of  the  opposite  valve,  communicating  at 

<?     <?    O     o     O 

J  K 

Fig.  20. — A  series  of  eleven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Rhynchopora  hamburgensis  (X  2V2) ;  A  to  E,  the  pedicle  valve,  showing  the 
dental  lamellae;  F  to  K,  the  brachial  valve,  showing  the  undivided  hinge-plate, 
the  median  septum,  and  covered  crural  cavity. 

the  apex  with  the  foramen  which  encroaches  upon  the  beak,  deltidial 
plates  not  observed;  plications  simple,  rounded  or  subangular,  originating 
at  the  beak,  from  three  to  six,  more  usually  four  or  five,  occupy  the  sinus, 
and  about  five  each  lateral  slope.  Internally  the  hinge  teeth  are  sup- 
ported by  a  pair  of  short  dental  plates  which  quickly  become  obsolete  in 
front  of  the  articulation  of  the  hinge. 


RHYNCHOPORA  229 

Brachial  valve  more  convex  than  the  pedicle,  becoming  gibbous  in 
mature  shells,  the  umbonal  region  flattened  longitudinally  or  sometimes 
with  a  slight  mesial  depression,  the  greatest  convexity  at  or  near  the  front 
margin,  the  surface  sloping  from  the  point  of  greatest  convexity  to  the 
beak  with  an  increasing  curvature  and  with  a  more  or  less  abrupt  curva- 
ture to  the  front,  laterally  from  the  median  line  the  surface  is  at  first 
gently  convex  but  soon  curves  abruptly  to  the  margins;  the  mesial  fold 
obsolete  in  the  posterior  half  of  the  valve  and  only  moderately  or  not  at 
all  differentiated  anteriorly;  the  beak  broad,  incurved  beneath  that  of  the 
opposite  valve;  the  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve  and  alternate  with  them.  Internally  the  cardinal  process 
is  lacking  and  the  hinge-plate  is  undivided,  although  the  median  portion 
is  differentiated  from  the  lateral  portions,  it  being  thinner  and  usually 
either  a  little  concave  or  a  little  convex ;  a  median  septum  is  present 
at  the  beak  which  is  soon  divided,  one  branch  supporting  each  of  the 
lateral  divisions  of  the  hinge-plate,  but  because  of  the  continuous  hinge- 
plate  the  pit  between  the  divisions  of  the  septum  is  not  an  open 
crural  cavity  as  in  Camaroto&chia,  but  is  a  covered  excavation  open  only 
towards  the  front ;  a  little  posterior  to  the  articulation  of  the  hinge,  the 
median  septum  and  its  divisions  which  support  the  hinge-plate  become 
discontinuous,  the  septum  continuing  as  a  gradually  disappearing  ridge 
for  about  one-fourth  the  length  of  the  valve  from  the  posterior  extremity. 

Surface  of  both  valves,  apart  from  the  plications,  nearly  or  quite 
smooth,  except  for  a  few  obscure  lines  of  growth  near  the  anterior  margin 
of  adult  shells.  The  shell  structure  is  minutely  punctate  and  in  at  least 
one  specimen  the  perforations  are  arranged  in  longitudinal  rows,  a  single 
row  upon  each  slope  of  each  plication. 

Remarks. — This  species  occurs  abundantly  in  the  Hamburg  oolite 
of  Kinderhook  age,  at  Hamburg,  Calhoun  County,  Illinois.  Externally, 
it  somewhat  resembles,  in  size  and  general  form,  the  CamarotoscJiia 
dioutraucnsis  from  the  Chouteau  limestone,  but  its  plications  are  less 
angular,  its  fold  and  sinus  are  less  abruptly  differentiated  from  the 
lateral  slopes,  and  its  beak  is  less  incurved  and  more  produced  posteriorly. 
Internally  the  two  forms  are  fundamentally  different,  E.  hamhurgensis 
having  the  continuous  hinge-plate  of  the  genus  Rhynchopora,  while  in  C. 
chouteaumsis  the  hinge-plate  is  medially  divided  and  the  characters  are 
those  of  Comoro! a  chin.  The  two  species  are  also  differentiated  by  the 
punctate  shell  structure  of  N.  hamhurgensis. 

The  internal  characters  of  the  species  have  been  determined  by  the 
study  of  serial  sections  made  by  grinding  detached  valves.  These  de- 
tached valves  have,  of  course,  been  subjected  to  accident  during  depo- 
sition, and  in  no  case  have  the  crura  been  detected,  although  they  were 
undoubtedly  present  as  anterior  prolongations  from  the  lateral  divisions 
of  the  hinge-plate.     In  some  of  the  specimens  examined  the  median  por- 


230 


MISSISSIPPI  \\    BH  veillHi'ODA 


lion  of  the  hinge-plate  has  also  been  destroyed,  this  part  being  distinctly 
thinner  and  more  delicate  than  the  Lateral  portions  and  therefore  much 
more  easily  destroyed.  The  continuous  hinge-plate  has  been  observed  in  a 
sufficient  number  of  individuals,  however,  to  make  it  certain  that  that  was 
the  normal  condition  of  (he  species.  The  punctate  structure  of  the  shell 
is  an  obscure  feature  and  in  many  individuals  it  cannot  be  detected  at  all 
on  accounl  of  the  condition  of  preservation  of  the  shell.  It  is  occasionally 
shown,  however,  and  in  the  specimen  in  which  it  is  best  exhibited  the 
perforations  are  not  distributed  uniformly  over  the  entire  shell  but  occur 
in  longitudinal  lines,  one  upon  each  lateral  slope  of  each  plication.  This 
is  probably  the  normal  condition  towards  the  beak  but  it  is  possible  that 
they  become  more  scattered  towards  the  anterior  margin  of  the  shell. 
Horizon. — Hamburg  oolite  of  the  Kinderhook. 

Kiivnciioi'oka   lHSTiiLosA    (White) 

Plate  XXIX,  Figs.  14-18 ;  Plate  XXIV,  Fig.  82 

1860.     Rhynchonella  pustulosa,  White,  Jour.  Boston  Soc.  Nat.  Hist.,  vol.  7, 
p.  236. 

1894.  Rhynchopora  pustulosa  Hall  and  Clarke,  Int.  to  Study  of  Braeh., 

pt.  2,  pi.  44,  figs.  26-29. 

1895.  Rhynchopora  pustulosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  58,  figs.  1-4. 
1901.     Rhynchopora  pustulosa  Weller,   Trans.   St.  Louis  Acad.   Sci.,  vol. 

11,  p.  157,  pi.  13,  figs.  4-6. 
1904.     Rhynchopora   pustulosa    Greger,   Am.    Geol.,    vol.   33,    p.    298-299, 

figs.  10-12. 
1910.     Rhynchopora  pustulosa  "Weller,   Bull.   Geol.   Soc.   Am.,  vol.  21,   p 

514,  fig.  16. 
Description.— Shell  below  medium  size,  subpyramidal  in  form,  wider 
than  long,  the  greatest  width  near  or  in  front  of  the  mid-length  of  the 
shell,  the  postero-lateral  margins  a  little  concave,  meeting  at  the  beak  in 
an  obtuse  angle,  the  lateral  margins  rounded,  the  anterior  margin  nearly 
straight  or  gently  convex.  The  dimensions  of  a  nearly  perfect  specimen 
are :  length  12.3  mm.,  width  12.6  mm.,  thickness  10.3  mm.,  width  of  the 
sinus  in  front  8.5  mm. 

Pedicle  valve  convex  in  the  umbonal  region  with  a  sigmoidally  curved 
slope  to  the  cardinal  margin,  to  the  antero-lateral  margin  the  surface  is 
gently  convex  and  from  the  beak  to  the  front  margin  along  the  median 
line  it  is  strongly  arched  in  nearly  a  semicircle ;  the  mesial  sinus  is  obsolete 
in  the  posterior  half  of  the  valve,  it  originates  near  or  in  front  of  the 
middle  of  the  valve  as  a  broad,  shallow,  flattened  depression  and  continues 
as  such  to  the  anterior  margin,  anteriorly  it  is  produced  in  a  broad, 
lingual  extension  rounded  in  front  with  a  serrate  margin,  wdiose  surface 
in  front  lies  in  nearly  a  right  angle  to  the  plane  of  the  valve ;  the  beak 
large,  moderately  incurved,  perforated  by  a  large,  subcircular  foramen ; 


BHYNCHOPORA  231 

the  dellhyrium  broadly  triangular,  nearly  filled  by  the  beak  of  the 
opposite  valve,  communicating  at  its  apex  with  the  foramen  which  en- 
croaches upon  the  beak  of  the  valve;  plications  rather  coarse,  rounded 
or   subangular,    simple,    originating   at    the    beak,    three    or   rarely    four 


oO 


^  <a>    <&   <2>    <2?   r^y 

KZ7  ^7  <^y 

H  I  J 

Fig.  21. — A  series  of  ten  cross-sections  of  the  rostral  portion  of  the  shell  of 
Rhynchopora  pustulosa  (X  2%),  only  the  first  two  (A  and  B)  with  the 
pedicle  valve;  sections  C  to  J  show  the  undivided  hinge-plate,  the  median 
septum,  and  covered  crural  cavity. 

occupying  the  mesial  sinus,  and  from  four  to  six  each  lateral  slope, 
those  towards  the  postero-lateral  margins  becoming  faint  or  almost 
obsolete,  the  plications  in  the  sinus  marked  by  a  slight  median  groove 
for  some  distance  back  from  the  anterior  margin.  Internally  the  hinge- 
teeth  are  supported  by  a  pair  of  dental  lamellae  whose  length  is  equal 
to  from  one-fifth  to  one-fourth  the  length  of  the  valve. 

Brachial  valve  much  more  convex  than  the  pedicle,  becoming  gibbous 
in  front,  the  surface  sloping  with  a  long,  regular,  or  an  inci-easing  curva- 
ture, from  the  highest  point  to  the  beak,  and  with  a  short,  usually  more 
convex  curvature  to  the  anterior  margin,  the  lateral  slopes  strongly 
convex  from  beak  to  front,  the  anterior  slope  more  abrupt,  and  curving 
abruptly  to  the  lateral  margins ;  mesial  fold  obsolete  in  the  posterior 
half  of  the  valve  and  only  slightly  differentiated  in  front ;  the  beak 
incurved  beneath  that  of  the  opposite  valve ;  the  plications  similar  in 
form  and  number  to  those  of  the  opposite  valve.  Internally  the  cardinal 
process  is  absent  and  the  hinge-plate  is  undivided ;  a  conspicuous  median 
septum  is  present  which  extends  one-third  the  length  of  the  valve  or 
more  from  the  beak,  posteriorly  the  median  septum  is  divided,  the  two 
branches  supporting  the  hinge-plate  and  forming  with  it  a  crural  cavity, 
triangular  in  cross  section,  which  is  open  only  towards  the  front,  the 
divided  septum  continues  to  the  position  of  the  articulation  of  the  hinge, 
beyond  which  the  septum  is  free,  the  hinge-plate  is  continued  anteriorly 
in  the  crura. 

Aside  from  the  plications  the  surface  of  both  valves  is  marked  by 
concentric  lines  of  growth  which  are  of  irregular  strength  and  are 
irregularly  arranged,  usually  being  inconspicuous.  The  shell  structure 
is  finely  and  closely  punctate. 


232  MISSISSI1T1AN    BRACHIOPODA 

Remarks. — The  punctate  structure  of  the  shell  is  commonly  rather 
obscure  in  examples  of  (his  species  which  have  come  under  observation. 
The  interna]  structures  of  the  rostral  portion  of  the  brachial  valve,  how- 
ever, especially  the  undivided  binge-plate,  always  seem  to  be  present  in 
specimens  which  are  clearly  punctate,  and  it  is  believed  that  they  are 
;ill  congeneric. 

Honzon.^Kinderhook. 

Iv'ns  NCHOPORA   BEECHERI   I  rreger 

Plate  XXIX,  Figs.  31-38 

1!H)4.     Rhynchopora  beecheri  Greger,  Am.  Geol.,  vol.  ''5:5,  p.  297,  figs.  4-9. 
1910.     Rhynchopora  beecheri  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21,  p.  515. 

Description. — Shell  below  medium  size,  triangularly  subovate  in  outline, 
subpyramidal  in  form,  broader  than  long  in  adult  individuals,  the  greatest 
breadth  near  the  mid-length  of  the  shell.  The  postero-lateral  margins 
nearly  straight  or  gently  convex,  meeting  at  the  beak  in  an  obtuse  angle, 
the  Lateral  margins  rounded,  the  anterior  margin  usually  nearly  straight. 
The  dimensions  of  a  nearly  complete  internal  cast  are :  length  10.5  mm., 
width  12.8  nun.,  thickness  10  mm.,  width  of  sinus  in  front  8  mm. 

Pedicle  valve  depressed  convex  in  the  umbonal  region  with  the  surface 
flattened  or  gently  convex  towards  the  antero-lateral  margins,  the  serrate 
lateral  margins  abruptly  deflected  towards  the  opposite  valve;  along  the 
median  line  the  surface  is  gently  convex  to  near  the  anterior  border  of 
the  shell  and  is  there  abruptly  curved  towards  the  opposite  valve ;  the 
mesial  sinus  originates  near  or  a  little  back  of  the  middle  of  the  valve 
as  a  rather  broad,  shallow  depression,  usually  a  little  convex  trans- 
versely across  the  bottom,  becoming  gradually  deeper  anteriorly  and 
curving  rather  abruptly  towards  the  opposite  valve  as  it  approaches  the 
anterior  margin  of  the  shell,  produced  in  a  broad  lingual  extension  with 
a  nearly  straight  and  deeply  serrate  distal  margin  whose  surface  in  front 
lies  in  nearly  a  right  angle  to  the  plane  of  the  valve ;  the  beak  rather 
broad  and  but  little  incurved,  perforated  by  a  subcircular  foramen ;  the 
delthyrium  broadly  triangular  and  nearly  filled  by  the  beak  of  the  oppo- 
site valve ;  plications  rounded  or  subangular,  simple,  originating  in  the 
umbonal  region  on  internal  casts  but  probably  continuing  to  the  beak 
upon  the  surface  of  the  shell,  from  four  to  six  occupy  the  sinus  and 
from  five  to  eight  each  lateral  slope.  Internally  the  hinge-teeth  are 
supported  by  a  pair  of  dental  lamellae  which  extend  from  one-third  to 
one-half  the  length  of  the  valve. 

Brachial  valve  much  more  convex  than  the  pedicle,  becoming  gibbous 
anteriorly  in  adult  specimens,  the  surface  slopes  from  the  point  of  greatest 
convexity  posteriorly  in  a  long  convex  curve  which  increases  towards  the 
beak,  and  in  a  short,  more  abrupt  curve  to  the  anterior  margin,  trans- 


RHYNCHOPORA  233 

versely  from  the  median  line  the  surface  is  at  first  gentry  convex  and 
then  curves  abruptly  to  the  lateral  margins,  the  curvature  being  a  little 
broken  towards  the  front  by  the  differentiation  of  the  median  fold,  the 
lateral  slopes  are  strongly  arched  from  beak  to  front  with  a  more  abrupt 
curvature  to  the  front;  the  mesial  fold  is  obsolete  in  the  posterior  half 
of  the  valve  and  is  but  moderately  elevated  above  the  lateral  slopes  in 
front ;  the  beak  incurved  beneath  that  of  the  opposite  valve.  Internally 
the  cardinal  process  is  absent  and  the  hinge-plate  is  undivided;  a  strong 
median  septum  is  present  which  is  divided  posteriorly,  each  branch  sup- 
porting one  side  of  the  hinge-plate,  between  the  divisions  of  the  septum 
is  a  crural  cavity  triangular  in  cross  section,  covered  on  one  side  by 
the  hinge-plate  and  open  only  towards  the  front,  anteriorly  the  septum 
is  free  and  reaches  from  one-third  to  one-half  the  length  of  the  valve. 

The  surface  markings  of  the  shell,  aside  from  the  plications,  are  not 
clear  on  the  internal  casts,  but  fragments  of  external  moulds  indicate 
that  it  was  nearly  or  quite  smooth.  The  shell  structure  is  finely  and 
closely  punctate,  the  punctae  being  much  more  abundant  upon,  and  seem 
sometimes  to  be  confined  to,  the  tops  of  the  plications.  The  punctae  render 
the  surface  of  the  internal  casts  finely  papillose,  and  when  the  internal 
cast  and  mould  of  the  exterior  are  examined  together  the  two  surfaces 
are  joined  bjr  innumerable,  minute,  transverse  pillars  which  are  the 
siliceous  casts  of  the  perforations  through  the  shell. 

Remarks. — This  species  resembles  R.  pustulosa  but  has  somewhat  finer 
and  more  numerous  plications,  and  the  entire  aspect  of  the  shell  is  more 
angular  in  form.  The  internal  characters  of  the  species  are  identical  in 
all  fundamental  respects,  but  the  dental  lamella?  of  the  pedicle  valve 
are  somewhat  longer,  and  the  divided  portion  of  the  septum  of  the 
brachial  valve  seems  to  continue  further  towards  the  front  in  R.  beecheri. 
The  species  is  most  commonly  preserved  as  internal  casts  and  external 
moulds  in  the  cherts  of  the  Keokuk  limestone,  and  it  has  not  been  observed 
in  any  other  condition  by  the  writer.  The  punctate  character  of  the 
shell  and  the  internal  rostral  characters  are  easily  recognized  in  the  chert 
specimens. 

Horizon.— Residual  Keokuk  chert. 

Rhynchopora  persinuata  (Winchell) 
Plate  XXX,  Figs.  1-6 

1865.     Rhynchonella   persinuata   Winchell,    Proe.    Acad.  Nat.   Sci.  Phil., 

p.  121. 
1883      Ca/marophoria  occidentalis  Miller,  Jour.  Cinn.  Soc.  Nat.  Hist.,  vol. 

4,  p.  313,  pi.  7,  figs.  7-7b. 
1901.     Camarotcechia  persinuata  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol. 

11.  p.  197,  pi.  19,  fig.  5. 


234  M  IssismI'I'IAN    BRACHIOPODA 

L909.     Camarotachia   persinuata   Weller,   Bull.   Geol.   Sue.   Ant.,  vol.    20, 

p.  302,  pi.  12,  figs.  24-25. 
1910.     Bhynchopora  persinuata  Weller,  Bull.  Geol.  Soe.  Am.,  vol.  21,  p. 

515. 

Description.  Shell  below  medium  size,  subpyramidaal  in  form,  wider 
than  Long,  the  postero-lateral  margins  meeting  al  the  beak  in  an  ol)tusc 
angle,  the  lateral  margins  rounded,  the  anterior  margin  straight.  The 
dimensions  of  an  incomplete  internal  casl  arc:  length  17  mm.,  width  20 
nun.,  thickness  1:1.7  mm.,  width  of  sinus  in  front   11.5  mm. 

Pedicle  valve  depressed  convex  in  the  posterior  half,  with  the  surface 
flattened  or  gently  convex  to  the  antero-lateral  margins  and  somewhat 
abruptly  curved  towards  the  opposite  valve  as  it  approaches  the  postero- 
lateral margins,  along  the  median  line  the  surface  is  gently  convex  from 
the  beak  to  near  the  anterior  margin  where  it  is  abruptly  curved  towards 
the  opposite  valve;  mesial  sinus  originating  near  the  middle  of  the  valve 
as  a  shallow,  flattened  depression  which  becomes  gradually  deeper  ante- 
riorly, towards  the  front  it  curves  abruptly  towards  the  opposite  valve 
and  is  produced  in  a  broad,  flat,  lingual  extension  whose  surface  lies  in 
nearly  a  right  angle  to  the  plane  of  the  valve  and  whose  front  margin  is 
deeply  serrate;  the  beak  is  small,  sharply  pointed,  moderately  incurved 
and  rather  conspicuously  extended  beyond  the  opposite  valve  posteriorly; 
the  delthyrium  is  broadly  triangular,  the  deltidial  plates  and  foramen 
not  observed ;  the  plications  rounded  or  subangular,  simple,  originating 
at  the  beak,  about  seven  usually  present  in  the  sinus  and  about  seven  or 
eight  upon  each  lateral  slope,  towards  the  anterior  margin  of  the  valve 
they  are  frequently  marked  by  a  faint  median  longitudinal  groove.  In- 
ternally the  hinge-teeth  are  supported  by  dental  lamella?  which  extend 
from  one-fourth  to  one-third  the  length  of  the  valve  anteriorly  from  the 
beak. 

Brachial  valve  much  more  convex  than  the  pedicle,  becoming  gibbous 
in  front,  flattened  in  the  umbonal  region  and  sometimes  with  a  slight, 
longitudinal,  median  depression,  the  surface  sloping  with  a  long,  gently 
convex  curvature  to  the  front,  the  lateral  portions  of  the  valve  strongly 
convex  longitudinally  the  anterior  curvature  being  more  abrupt,  and 
curving  abruptly  to  the  lateral  margins ;  mesial  fold  obsolete  in  the  pos- 
terior half  of  the  valve  and  only  moderately  elevated  above  the  lateral 
slopes  in  front ;  the  beak  strongly  incurved  beneath  that  of  the  opposite 
valve ;  the  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve,  and  frequently  grooved  in  a  similar  manner  towards  the  anterior 
margin.  The  internal  characters  of  the  species  are  not  sufficiently  well 
known,  but  the  cardinal  process  seems  to  be  absent,  and  the  hinge-plate 
seems  to  be  undivided,  a  median  septum  is  present  which  is  divided  pos- 
teriorly, each  division  supporting  one  side  of  the  hinge-plate,  the  cavity 
between  the  divisions  of  the  septa  apparently  does  not  form  an  open  crural 


RHYNCHOPORA  235 

cavity,  but  is  covered  by  the  median  portion  of  the  hinge-plate,  being 
open  only  towards  the  front,  the  median  septum  continues  anteriorly  from 
the  beak  for  about  one-fourth  the  length  of  the  valve. 

The  fine  surface  markings  are  obscure  upon  all  specimens  examined, 
but  occasional,  rather  inconspicuous  concentric  lines  of  growth  are  pres- 
ent towards  the  anterior  margin.     The  shell  structure  is  finely  punctate. 

Ii'i  marks. — In  general  form  this  species  approaches  very  closely  to 
R.  c-ooperensis,  the  most  conspicuous  difference  being  in  its  somewhat  finer 
plications,  and  even  in  this  character  it  grades  into  the  other.  The  two 
forms  should  perhaps  be  considered  as  synonyms,  but  the  only  typical 
representatives  of  R.  persinuuta  have  been  found  at  a  somewhat  higher 
geological  horizon  than  the  typical  R.  cooper ensis,  and  the  two  forms  have 
in  consequence  been  considered  as  distinct.  Furthermore  the  punctate 
shell  structure  has  not  been  actually  observed  in  R.  cooperensis.  The 
shell  which  was  described  by  Miller  as  Camarophoria,  occidentalis  from  Lake 
Valley,  New  Mexico,  is  clearly  identical  with  R.  persinnata.  Authentic 
examples  of  Miller's  species  from  the  typical  locality  exhibit  none  of 
tht  characters  of  Camarophoria,  but  they  do  agree  in  all  respects  with 
authentic  specimens  of  Winched 's  species.  The  punctate  structure  of  the 
shell  is  commonly  obscure  and  frequently  cannot  be  detected  at  all.  The 
type  of  the  species  is  an  internal  cast  in  a  rather  coarse  dolomitic  material, 
which  is  incapable  of  preserving  such  characters,  but  in  one  specimen 
from  the  Fern  Glen  formation  of  St.  Louis  County,  Missouri,  the  puncta- 
tion  of  the  shell  can  be  clearly  seen  on  parts  of  the  surface.  The  speci- 
men, which  exhibits  this  character  best,  is  one  of  those  from  Lake  Valley, 
New  Mexico.  The  internal  characters  of  the  rostral  portion  of  the 
brachial  valve  have  not  been  observed  by  sectioning  authentic  specimens 
from  the  typical  locality,  both  because  such  specimens  are  too  uncommon 
and  because  their  condition  of  preservation  is  not  favorable.  One  excel- 
lent internal  cast  of  this  portion  of  the  shell  from  the  typical  locality, 
clearly  shows,  however,  the  presence  of  the  undivided  hinge-plate  which 
is  characteristic  of  the  genus.  The  median  septum  divided  posteriorly 
is  also  clearly  shown  in  this  specimen,  but  the  divisions  of  the  septa  seem 
to  give  support  to  the  hinge-plate  to  a  point  somewhat  farther  anterior  in 
position  than  in  R.  cooperensis,  but  such  a  character  may  be  expected  to 
vary  even  within  a  single  species. 

Horizon. — Kinderhook. 

Rhynchopora   ?  cooperensis  (Shumard) 
Plate  XXX,  Figs.  7-15 ;   ?  22-25 

1855.     Rhynchnella   Cooperensis  Shuni.,   I   and  II  Rep,   Geol.   Surv.   Mo., 

p.  204,  pi.  C,  figs.  4a-d. 
1894.     RJiynchonclla  cooperensis  Keyes,  Mo.   Geol.   Surv.,   vol.   5,  p.   101. 
1910.     Rhynchopora   ?  cooperensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  21, 

p.  515,  fig.  18. 


236 


\l  [SSISSIPPIAN    HKACIIIOl'ODA 


Description.  Slid!  usually  below  medium  size,  broader  than  long,  the 
postero-lateral  margins  meeting  ;ii  the  beak  in  an  olit use  angle,  the  lateral 
margins  rounded  and  the  anterior  margin  nearly  straight.  The  dimen- 
sions of  a  rather  small  bu1  nearly  complete  specimen  are:  Length  14. (i ., 

width  17  mm.,  thickness  12  mm.,  width  of  sinus  in  Eront  !'..r)  mm. 

Pedicle  valve  depressed  convex  in  the   posterior  half  and  flattened  or 

gently  convex   to   the  antero-latt-ral    margins,  along    the    median    line  the 

surface  is  gently  convex  to  near  the  anterior  margin  of  the  shell  where 
it  is  strongly  curved  towards  the  opposite  valve,  along  the  postero-lateral 

margins  towards  the  beak,  the  edge  of  the  valve  is  inflected  towards  the 
opposite  valve;  mesial  sinus  originating  near  the  middle  of  the  valve  as 
a  shallow,  flattened  depression,  il  is  but  little  depressed  to  near  the  an- 
terior margin  of  the  valve  where  it  is  rather  abruptly  and  strongly  curved 


Fig.  22. — A  series  of  eight  cross-sections  of  the  rostral  portion  of  the  shell  of 
Rhynchopora  f  cooperensis  (X  2%),  showing  the  undivided  hinge-plate,  and 
the  consequently   covered   crural   cavity. 

towards  the  opposite  valve  and  produced  in  a  broad  lingual  extension 
whose  surface  lies  in  nearly  a  right  angle  to  the  plane  of  the  valve,  and 
which  is  deeply  serrate  at  the  distal  line  of  junction  with  the  opposite 
valve ;  beak  rather  small,  pointed,  slightly  incurved,  rather  conspicuously 
protuberant  beyond  that  of  the  opposite  valve,  pierced  by  a  small,  sub- 
circular  foramen;  delthyrium  broadly  triangular  and  communicating  with 
the  foramen  at  its  apex,  the  deltidial  plates  not  observed ;  plications  sub- 
angular  or  rounded,  simple  and  originating  at  the  beak,  from  four  to  six 
occupy  the  sinus  with  about  six  others  upon  each  lateral  slope  and  some- 
times one  or  two  very  faint  ones  towards  the  postero-lateral  margins,  the 
plications  of  the  sinus  are  sometimes  medially  grooved  towards  the  front. 
Internally  the  hinge-teeth  are  supported  by  dental  lamella?  which  extend 
anteriorly  from  the  beak  for  about  one-fourth  or  more  of  the  length  of  the 
valve. 


RHYNCHOPORA  237 

Brachial  valve  much  more  strongly  convex  than  the  pedicle,  becoming 
ventricose  towards  the  front,  the  umbonal  region  mesially  flattened 
or  with  a  shallow,  longitudinal  depression  which  sometimes  continues  to 
the  front  of  the  valve,  the  surface  sloping  with  an  increasing  curvature 
from  the  point  of  greatest  curvature  to  the  beak,  and  with  a  short  and 
rather  abrupt  curvature  to  the  front,  the  lateral  slopes  gently  convex  on 
either  side  of  the  fold  and  then  curving  abruptly  to  the  margin  both  later- 
ally and  anteriorly;  the  mesial  fold  obsolete  in  the  posterior  half  of  the 
shell  and  only  moderately  elevated  above  the  lateral  slopes  in  front ; 
beak  broadly  pointed  and  strongly  incurved  beneath  that  of  the  opposite 
valve;  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve,  those  of  the  lateral  slopes  strongly  arched  longitudinally  and  some- 
times with  a  slight  median  groove  in  front.  Internally  the  cardinal  pro- 
cess  is  wanting;  the  hinge-plate  is  undivided  but  with  the' transversely 
convex  median  portion  differentiated  from  the  lateral  portions  anteriorly, 
at  the  apex  of  the  beak  a  median  septum  divided  above  supports  the  in- 
itial portion  of  the  hinge-plate,  but  the  connection  between  the  septum 
and  the  hinge-plate  is  very  short  and  the  septum  itself  rapidly  becomes 
lower  and  disappears  at  about  one-fourth  the  length  of  the  valve  from  the 
beak,  the  lateral  portions  of  the  hinge-plate  are  produced  anteriorly  into 
the  crura. 

Surface  of  both  valves  marked  by  fine,  more  or  less  regular,  concentric 
stria?  and  by  occasional  stronger  lines  of  growth,  the  growth  lines  being 
more  conspicuous  towards  the  anterior  margin.  The  shell  structure  prob- 
ably punctate. 

Remarks.  —  This  species  is  referred  with  a  query  to  the  genus  Rhyncho- 
pora, because  the  punctate  shell  structure  has  not  been  observed.  The 
character  of  the  hinge-plate  of  the  brachial  valve,  undivided  as  it  is  to  the 
crural  bases,  agrees  with  the  structure  found  in  Rhynchopora,  this  undi- 
vided hinge-plate  being  unknown  in  any  other  of  our  Mississippian 
rhynchonelloid  shells.  The  species  most  closely  resembles  R.  persinuata 
in  which  the  punctate  structure  of  the  shell  has  been  clearly  observed,  and 
it  is  possible  that  the  two  forms  should  really  be  considered  as  synonyms. 
The  relationships  of  these  two  species  have  been  fully  considered  in  the 
discussion  of  R.  persinuata. 

Horizon. — Kinderhook  and  base  of  Burlington  limestone. 

Rhynchopora   ?  rowleyi  n.  sp. 
Plate  XXX,  Figs.  18-21 

1908.     Pugnax  missouriensis   ?  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol. 
8,  2nd  ser.,  p.  81.  pi.  17,  figs.  60-62. 

Description.  —  Shell  of  about  medium  size,  wider  than  long,  transversely 
subelliptical    in    outline,    the    greatest    width    near   the    mid-length,    the 


238  MISSISSIPPIAN    BRACHIOPODA 

postero-lateral  margins  a  little  concave,  meeting  ;ii  the  beak  in  an  obtuse 
angle,  the  lateral  margins  rounded,  the  anterior  margin  emarginate.  The 
dimensions  of  ;i  nearly  perfed  specimen,  the  holotype,  arc:  length  of 
pedicle  valve  18  mm.,  length  of  brachial  valve  17.8  mm.,  greatesl  width 
23.2  nun.,  thickness  15.6  nun.,  width  of  sinus  in  front   VAM  mm. 

Pedicle  valve  depressed  convex,  the  greatesl  depth  being  posterior  to 
the  middle  near  the  umbonal  region,  the  surface  curving  gently  to  the  an- 
tero-lateral  and  lateral  margins,  becoming  more  strongly  convex  to  the 
postero-lateral  and  cardinal  margins;  mesial  sinus  originating  near  or  a 
little  back  of  the  middle  of  the  valve,  broad  and  shallow  at  first,  becom- 
ing rapidly  deeper  towards  the  front  where  it  is  produced  in  an  elongate 
and  broad  lingual  extension  directed  at  about  a  right  angle  to  the  plane 
of  the  valve  and  with  a  strongly  serrate  anterior  margin;  beak  small, 
sharply  pointed,  moderately  incurved  and  coming  nearly  in  contact  with 
the  umbo  of  the  opposite  valve;  the  delthyrium  broadly  triangular,  nearly 
filled  by  the  beak  of  the  opposite  valve.  The  simple  plications  are  rounded 
posteriorly,  becoming  more  subangular  anteriorly,  seven  or  eight  occupy 
each  lateral  slope  of  the  valve  and  six  the  mesial  sinus.  Internally  the 
hinge-teeth  are  supported  by  strong  dental  lamella?  which  diverge  a  little 
more  widely  than  the  lateral  margins  of  the  sinus  and  extend  anteriorly 
more  than  one-third  the  length  of  the  valve. 

Brachial  valve  strongly  convex,  the  greatest  depth  anterior  to  the 
middle,  the  surface  curving  abruptly  to  the  antero-lateral.  lateral,  and 
postero-lateral  margins,  becoming  inflected  to  the  cardinal  extremities; 
mesial  fold  originating  near  the  middle  of  the  valve,  flattened  on  top,  be- 
coming only  moderately  differentiated  from  the  general  curvature  of  the 
valve  towards  the  front ;  the  umbonal  region  prominent,  the  beak  strongly 
incurved  beneath  that  of  the  opposite  valve.  The  plications  more  angular 
than  those  of  the  opposite  valve  and  alternate  with  them,  those  reaching 
the  antero-lateral  margins  being  distinctly  grooved  along  their  median 
line  for  some  distance  back  from  the  margin.  The  internal  characters  of 
the  valve  are  not  sufficiently  known,  but  a  thin  median  septum  is  present 
which  reaches  nearly  to  the  middle  of  the  valve. 

The  finer  surface  markings  are  not  well  preserved  upon  the  specimen 
here  described,  but  they  apparently  consist  of  rather  fine  and  somewhat 
irregular  concentric  lines  of  growth  which  become  a  little  stronger  and 
more  crowded  towards  the  front.  No  punctate  shell  structure  has  been 
observed. 

Remarks. — Judging  from  its  external  characters  alone  this  species  seems 
to  be  congerenic  with  B.  persinuata,  and  the  character  of  the  dental 
lamella?  of  the  pedicle  valve  and  the  median  septum  of  the  brachial  valve 
also  agree  with  that  species.  It  is  not  known,  however,  that  the  brachial 
valve  possesses  an  undivided  hinge-plate  covering  the  crural  cavity,  a 
feature  which  is  characteristic  of  B.  pcrsimtata  and   other  species  which 


RHYNCHOPORA  239 

have  been  included  in  the  genus  Rhynchopora  in  this  volume.  The  ap- 
parent  absence  of  any  indication  of  punctate  shell  structure  is  op- 
posed to  the  inclusion  of  the  present  species  in  Rhynchopora,  but  this 
feature  is  likewise  very  obscure  in  R.  persinuata,  having"  been  observed, 
indeed,  in  only  a  tew  individuals,  and  even  in  those  it  is  not  always  beyond 
question,  while  in  /»'.  cooperensis,  another  closely  allied  species,  the  punc- 
tate shell  structure  has  never  been  observed.  For  the  present,  therefore, 
the  species  will  be  included  in  Rhynchopora  with  a  query.  The  species 
differs  from  R.  i><  rsiiiinita  in  its  somewhat  greater  proportionate  width 
and  consequent  coarser  plications  which  are  separated  by  relatively  shal- 
lower and  broader  furrows.  The  anterior  lingual  extension  of  the  pedicle 
valve  is  also  distinctly  concave  transversely  in  the  type,  giving  to  the 
anterior  margin  of  the  shell  a  distinctly  emarginate  outline,  while  in 
R.  persinuata  this  lingual  extension  is  flat  and  the  anterior  margin  of  the 
shell  consequently  straight. 

Horizon. — Louisiana  limestone. 

Rhynchopora    .'  perryensis  n.  sp. 
Plate  XXV,  Figs.  18-21 

Description. — Shell  small,  broadly  subovate  in  outline,  usually  a  little- 
wider  than  long,  the  greatest  width  near  the  mid-length  of  the  shell,  the 
postero-lateral  margins  nearly  straight  and  meeting  at  the  beak  in  an 
angle  of  from  105  to  110  degrees,  the  anterolateral  and  anterior  margins 
rounded.  The  dimensions  of  a  nearly  perfect  specimen  are :  length  of 
pedicle  valve  10.2  mm.,  length  of  brachial  valve  9.2  mm.,  greatest  width 
10.5  mm.,  thickness  8  mm.,  width  of  sinus  in  front  7.1  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  rather  narrowly  rounded 
transversely  across  the  median  line  with  the  surface  gently  convex  to  the 
antero-lateral  margins  and  curving  abruptly  to  the  postero-lateral  mar- 
gins, from  the  beak  to  the  anterior  margin  along  the  median  line  the 
surface  describes  nearly  a  semicircular  curve ;  mesial  sinus  originating 
near  the  middle  of  the  valve,  nearly  flat  or  slightly  convex  transversely 
in  the  bottom,  produced  anteriorly  in  a  rounded  lingual  extension  of 
greater  or  less  length ;  beak  sharply  pointed  and  strongly  incurved,  the 
apex  coming  in  contact  with  the  umbo  of  the  opposite  valve,  the  delthy- 
rium  hidden  by  the  incurvature  of  the  beak ;  plications  simple,  obsolete 
towards  the  beak  but  originating  in  the  umbonal  region,  they  are  low 
and  broadly  rounded  posteriorly,  becoming  more  angular  towards  the 
front,  two  or  three,  rarely  four,  occupy  the  bottom  of  the  mesial  sinus, 
the  sloping  sides  of  the  sinus  being  entirely  nonplicate ;  upon  each  lateral 
slope  of  the  valve  are  from  four  to  six  plications  which  grow  successively 
smaller  towards  the  cardinal  extremities,  the  last  one  or  two  being  very 


240 


M  [SSISSIPPIAN    HHACIIIOI'ODA 


r.iini  ;  fine,  regular,  concentric  lines  of  growth  cover  the  entire  surface  of 
the  valve,  becoming  somewhat  stronger  towards  the  outer  margin.  In- 
ternally  the  dental  lamella'  are  short. 

Brachial  valve  much  more  strongly  convex  than  the  pedicle,  the  great- 
est convexity  near  the  anterior  margin,  the  surface  sloping  with  a  long, 
gently  convex  curve  from  the  poinl  of  greatesl  elevation  to  the  beak,  a 
portion  of  this  slope  in  the  middle  pari  of  the  valve  being  nearly  straight, 
along  the  median  line  in  the  umbonal  region  towards  the  beak,  the  sur- 
face is  a  little  impressed  in  a  slight  median  sinus,  the  slopes  from  the 
median  line  to  the  Lateral  margins  of  the  valve  arc  convex  and  rather  ab- 
rupt, with  a  slighl  interruption  in  the  slope  anteriorly  at  the  lateral  bor- 
ders of  the  mesial  fold;  mesial  fold  originating  near  the  middle  of  the 
valve,  not  strongly  differentiated  from  the  general  convexity  except  near 
the  anterior  margin;  the  beak  strongly  incurved  beneath  that  of  the  op- 
posite valve;  the  plications  entirely  similar  in  form  and  number  to  those 
of  the  opposite  valve,  and  alternate  with  them,  and  the  concentric  lines 
of  growth  also  similar.  Internally  a  thin  median  septum  is  present  in  the 
rostral  portion  of  the  valve  which  divides  internally  and  is  joined  to  the 
two  lateral  divisions  of  the  hinge-plate,  the  resulting  crural  cavity  being 
very  broad  and  shallow.  The  hinge-plate  apparently  divided.  Shell 
structure  minutely  punctate. 

Remarks. — The  specimens  originally  used  in  the  description  of  this 
species  were  collected  by  Mr.  D.  K.  Greger  at  Landing  No.  76,  Perry 
County.  Missouri.  Since  the  description  was  written,  however,  some  ex- 
cellent examples  of  the  species  have  been  collected  from  the  Okaw  lime- 
stone of  the  Chester  group  in  Randolph  County,  Illinois,  which  clearly 
exhibit  a  distinctly  punctate  shell  structure.  A  re-examination  of  the 
Perry  County  examples  has  led  to  the  detection  of  the  same  structure 
upon  these  specimens,  although  it  is  very  obscure  and  has  been  almost  en- 
tirely obliterated  in  the  process  of  fossilization.  The  punctate  shell  struc- 
ture in  a  rhynchonelloid  shell  is  characteristic  of  Rlijj)icJtopora,  in  which 
genus  the  species  is  here  placed,  although  it  differs  in  some  particulars 
from  other  species  which  have  been  included  in  this  genus  in  this  report. 
In  all  the  other  species  of  Rhynchopora  here  recognized,,  the  hinge-plate 
of  the  brachial  valve  is  undivided,  the  crural  cavity  being  inclosed  above, 
but  in  this  species  the  hinge-plate  is  apparently  divided.  It  is,  of  course, 
possible  that  the  median  plate  joining  the  two  sides  of  the  hinge-plate 
was  very  delicate  and  easily  injured,  and  that  it  has  been  destroyed  in  the 
few  specimens  which  have  been  ground  down,  but  this  is  not  likely,  since 
all  of  the  specimens  so  examined  have  been  shells  with  both  valves  in  ar- 
ticulation. So  far  as  it  is  known,  the  internal  characters  of  the  species 
fire  identical  with  those  of  Camarotcpclua.  Another  character  in  which 
this  species  differs  from  other  members  of  the  genus  Rhynchopora  here 
recognized,  is  the  obsolescence  of  the  plications  in  the  posterior  portion 


CENTRONELLA  241 

of  the  shell,  in  this  respect  simulating  the  genera  Vuynax  and  Pugnoidcs. 
In  fact,  were  it  not  for  the  punctate  shell  structure  the  species  would  be 
placed  in  the  genus  Pugnoides  without  hesitation.  It  is  possible,  of 
course,  that  more  than  one  generic  group  of  rhynchonelloid  shells  de- 
veloped the  punctate  structure,  and  that  all  such  shells  should  not  be  re- 
ferred to  Ehynchopora,  but  until  the  internal  characters  of  the  genotype 
have  been  determined,  it  seems  unwise  to  erect  any  additional  genera. 
Horizon.  — ()k;\\x  limestone  of  the  Chester  group. 

Family  CENTRONELLID.E 
Genus  CEXTROXELLA  Billings 

Description.  —  Shell  small,  rostrate,  plano-convex  or  concavo-convex,  with 
smooth  valves.  Pedicle  valve  with  a  median,  longitudinal  ridge  from 
which  the  surface  slopes  more  or  less  abruptly  to  the  lateral  margins, 
the  beak  acute  and  incurved,  perforated  at  its  apex  by  a  subcircular  fora- 
men, the  delthyrium  closed  by  a  pseudodeltidium.  Brachial  valve  con- 
cave transversely  by  reason  of  the  presence  of  a  median  sinus  which  is 
not  apparent  on  the  interior,  the  beak  small,  not  incurved.  Internally  the 
dental  sockets  are  broad,  bounded  interiorly  by  the  high  walls  of  the 
hinge-plate.  This  plate  is  divided  medially  by  a  deep  furrow  extending 
to  the  apex,  and,  therefore,  consists  of  two  processes  which  are  elevated, 
thickened  and  rest  on  the  bottom  of  the  valve.  From  the  anterior  face 
of  these  arise  the  crura  which  converge  for  a  short  distance,  and  expand 
to  form  two  broad,  acute  jugal  processes.  From  here  the  lateral  branches 
of  the  brachidium  curve  outward,  gradually  turning  from  a  vertical  to  a 
horizontal  position,  broaden  rapidly  and  unite  to  form  an  anterior  trian- 
gular plate  which  bears  a  median  ridge  where  the  two  lateral  branches 
are  conjoined. 

Remarks.— The  species  which  are  here  referred  to  the  genus  Centron- 
clhi.  are  so  placed  because  of  external  form  alone.  The  description  of  the 
brachidium  given  above  is  from  the  work  of  Hall  and  Clarke,  and  it  is  by 
no  means  certain  that  the  characters  of  these  Mississippian  species 
conform  to  the  definition  of  the  genotype. 

Centronella  louisianensis  n.  sp. 
Plate  XXX,  Figs.  26-29 

Description.— Shell  minute,  subovate  in  outline,  longer  than  wide,  the 
greatest  width  anterior  to  the  mid-length,  the  anterior  and  antero-lateral 
margins  describing  nearly  a  semicircle  or  slight^  truncated  in  front,  the 
postero-lateral  margins  nearly  straight  or  gently  convex,  meeting  at  the 
beak  in  an  acute  angle.  The  dimensions  of  a  perfect  specimen  are: 
length  of  pedicle  valve  2.9  mm.,  length  of  brachial  valve  2.5  mm.,  width  2.7 
nidi.,  thickness  1   mm. 


242  MISSISSIPPIAN     BRACHIOPODA 

Pedicle  valve  Longitudinally  subcarinate,  with  the  Lateral  slopes  gently 
convex,  the  curvature  becoming  more  abrupl  towards  the  cardinal  mar- 
gins, the  margins  incurved  between  the  cardinal  extremities  and  the  apex 
of  (lie  beak  to  form  a  small  pseudo-cardinal  area  lying  in  nearly  the  plane 
of  the  valve,  the  valve  arched  from  beak  to  front  along  the  median  line 
with  the  curvature  somewhat  more  abrupt  posteriorly,  the  greatest  depth 
of  the  valve  posterior  to  the  middle;  the  beak  prominent,  acutely  pointed, 
very  slightly  incurved,  projecting  notably  beyond  that  of  the  opposite 
valve;  delthyrium  broadly  triangular,  partially  closed  by  a  pair  of  delti- 
dial  plates  which  do  not  meet  al  the  median  line,  thus  leaving  a  triangular 
foramen   which    reaches    from   the  apex   to   the  base. 

Brachial  valve  less  convex  than  the  pedicle,  greatest  depth  posterior  to 
the  middle,  the  surface  curving  more  abruptly  to  the  cardinal  margins; 
beginning  just  in  front  of  the  nmbonal  region  a  shallow,  sub-angular  or 
rounded  mesial  sinus,  with  ill-defined  lateral  margins,  continues  with 
increasing  depth  to  the  front  margin;  lateral  slopes  of  the  valve  convex 
transversely  from  the  median  line  to  the  lateral  margins;  beak  obtusely 
pointed,  scarcely  or  not  at  all  incurved. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  more  or  less 
inconspicuous  concentric  lines  of  growth  which  are  sometimes  nearly 
obsolete. 

Remarks. — This  little  shell  resembles  the  associated  Trigeria  curreyi 
in  size  and  general  form,  but  differs  from  it  in  the  absence  of  plications 
and  commonly  in  the  less  angular  median  sinus  of  the  pedicle  valve.  In 
its  smooth  shell  it  resembles  the  associated  Selenella  pecliculus,  but  may 
be  easily  distinguished  from  it  by  its  subcarinate  pedicle  valve,  its  sinuate 
brachial  valve,  and  by  the  more  conspicuous  concentric  lines  of  growth. 
The  species  is  referred  to  the  genus  Centronella  because  of  its  external 
form  alone,  the  internal  chai'acters  of  neither  valve  being  known,  nor 
has  the  punctate  structure  of  the  shell  been  detected. 

Horizon.— Louisiana    limestone    of   the   Kinderhook. 

Centronella   ( ? )  emaciata  Rowley 
Plate  XXX,  Figs.  40-42 

1900.  Centronella  emaciata  Rowley,  Ami.  Geol.,  vol.  25,  p.  265,  pi.  5, 
figs.  48-50. 
Description.  —  Shell  small,  longer  than  wide,  ovate-siubpe,ntagonal  in 
outline,  the  greatest  width  posterior  to  the  mid-length ;  the  posterior 
lateral  margins  nearly  straight  and  meeting  at  the  beak  in  an  angle  of 
about  80  degrees,  posteriorly  the  margins  round  rather  abruptly  into  the 
gently  convex  antero-lateral  margins  which  in  turn  pass  gradually  into 
the  rather  short  but  more  convex  anterior  margin.  The  dimensions  of 
the  holotype  are :  length  of  pedicle  valve  12.3  mm.,  length  of  brachial 
valve  11.2  mm.,  greatest  width  9.8  mm.,  thickness  4.1  mm. 


SELENELLA  243 

Pedicle  valve  with  its  greatest  depth  a  little  posterior  to  the  middle, 
subcarinate  along  the  median  region  from  the  beak  nearly  to  the  front 
margin,  on  either  side  of  the  rather  narrowly  rounded  median  region  the 
surface  slopes  to  the  extreme  lateral  extremities  with  a  gently  concave 
curvature  producing  a  compression  of  the  valve  in  that  direction,  near  the 
posterolateral  margins  the  surface  is  abruptly  curved  towards  the  oppo- 
site valve,  becoming  inflected  to  the  cardinal  extremities,  from  the  highest 
point  to  the  front  margin  the  surface  is  gently  convex  and  to  the  beak 
a  little  less  gently  convex ;  mesial  sinus  absent,  the  subcarinate  median 
portion  of  the  valve  simulating  a  mesial  fold ;  the  beak  acutely  pointed, 
strongly  protuberant  beyond  that  of  the  opposite  valve,  nearly  erect,  the 
foramen  not  clearly  shown  in  the  type  but  apparently  small  and  encroach- 
ing upon  the  umbonal  region,  the  characters  of  the  delthyrium  and 
pseudodeltidium  hidden  in  the  specimen.  Internally  a  pair  of  dental 
lamella'  extend  anteriorly  from  the  beak  for  about  one-fifth  the  length  of 
the  valve  with  a  very  narrow  angle  of  divergence. 

Brachial  valve  much  flattened,  less  convex  than  the  pedicle,  the  greatest 
depth  posterior  to  the  middle,  the  surface  very  gently  convex  to  the 
antero-lateral  and  anterior  margins,  curving  more  abruptly  to  the  postero- 
lateral margins,  especially  as  it  approaches  the  margin ;  mesial  fold  or 
sinus  absent;  the  beak  moderately  incurved,  passing  beneath  the  delthy- 
rium of  the  opposite  valve. 

Shell  structure  minutely  punctate. 

Remarks. — In  general  outline  this  shell  resembles  Centronella  alveolata 
Hall  from  the  Onondaga  limestone  of  New  York,  but  it  is  a  smaller  and 
much  thinner  shell  with  the  pedicle  valve  less  arcuate  and  without  a 
median  sinus  in  the  brachial  valve.  The  internal  characters  of  this 
species,  aside  from  the  dental  lamella1  of  the  pedicle  valve,  are  unknown, 
though  it  can  be  affirmed  that  no  median  septum  is  present  in  the  brachial 
valve,  that  valve  being  so  exfoliated  in  the  type  specimen  that  it  would 
be  clearly  shown  if  present.  The  species  is  quite  certainly  not  a  true 
Centronella,  because  in  all  cases  where  the  form  of  the  brachidhun  is 
known  among  these  shells,  important  modifications  in  the  Centronella  type 
of  loop  have  become  fixed  before  the  beginning  of  Mississippian  time  but 
without  a  knowledge  of  the  characters  of  the  brachidium,  it  is  unwise 
to  propose  a  new  generic  division,  and  the  species  is  allowed  to  rest  in 
Centronella  with  a  query. 

Horizon. — Burlington  white  chert. 

Genus  SELENELLA  Hall 

Description. — Shell  small,  terebratuliform.  with  biconvex,  smooth  valves, 
subovate  in  outline.     Internally  the  brachidium  is  eentronelliform,  but 


L'44  MISSISSIPPIAN   BBACHIOPODA 

without   .interior  or  posterior  prolongation,  and  without  the  thickening 
along  1  hi'  symphysis  of  the   lateral  elements. 

Remarks. — The  only  species  of  this  genus  recognized  in  our  faunas 
is  so  small  that  il  has  been  impracticable  to  study  its  internal  characters 
by  means  of  serial  sections  as  has  been  done  ill  the  case  of  the  larger 
tonus,  hut  the  centronellid  character  of  the  brachidium  has  been  de- 
tected in  one  specimen  which  is  rilled  with  translucent,  crystalline 
calcite. 

Selenella  pediculus  (  Rowley) 

Plate  XXX,  Figs.  34-39 

linn.     Dielasma  (?)  pediculus  Rowley,  Am.  Geo!.,  vol.  27,  p.  350,  pi.  28, 

figs.  43-45. 
L908.     Dielasma  I  ?)  pediculus  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  80,  pi.  17,  figs.  57-5!i. 

Description. —  Shell  minute,  smooth,  subovate  in  outline,  longer  than 
wide,  the  greatest  width  near  or  posterior  to  the  mid-length,  the  anterior 
margin  regularly  rounded  or  slightly  truncated  in  the  middle,  pointed 
posteriorly.  The  dimensions  of  a  large  example  are:  length  of  pedicle 
valve  4  mm.,  length  of  brachial  valve  3.5  mm.,  greatest  width  3.2  mm., 
i  bickness  1.5  mm. 

Pedicle  valve  arched  from  beak  to  front  with  the  curvature  a  little 
more  abrupt  to  the  posterior  extremity,  also  arched  transversely  with 
the  lateral  slopes  a  little  flattened,  the  greatest  convexity  of  the  valve 
near  the  middle,  the  surface  incurved  towards  the  cardinal  extremities 
to  form  a  small,  pseudo-cardinal  area ;  mesial  portion  of  the  valve  not 
differentiated  except  sometimes  a  little  flattened  anteriorly ;  the  beak 
prominent,  pointed,  slightly  incurved,  projecting  conspicuously  beyond 
that  of  the  opposite  valve ;  delthyrium  large,  broadly  triangular,  par- 
tially closed  by  a  pair  of  deltidial  plates  which  sometimes  meet  towards 
the  base  of  the  delthyrium,  but  often  failing  to  meet  and  so  leaving 
a  triangular  opening  from  the  apex  to  the  base,  the  foramen  slightly 
or  not  at  all  encroaching  upon  the  beak  of  the  valve. 

Brachial  valve  depressed  convex,  its  depth  about  one-half  that  of  the 
pedicle  valve,  the  surface  curving  more  abruptly  towards  the  cardinal 
margin ;  mesial  portion  of  the  valve  not  distinctly  differentiated,  al- 
though it  is  rather  broadly  flattened;  the  beak  short,  obtusely  pointed, 
incurved  beneath  the  delthyrium  of  the  opposite  valve.  Internally  the 
brachidium  is  centronelloid  in  form,  without  anterior  or  posterior  pro- 
longation, being  essentially  of  the  type  characteristic  of  the  genus 
Selenella. 

Surface  of  both  valves  usually  entirely  smooth,  when  lines  of  growth 
are  present  they  are  very  faint  and  are  restricted  to  the  marginal 
portion. 


TRIGERIA  245 

Remarks. — The  brachidium  has  been  observed  in  but  a  single  example 
of  this  shell,  the  interior  of  which  specimen  is  filled  with  nearly  trans- 
parent ealeite.  In  this  specimen  the  brachidium  is  apparently  complete 
and  seems  to  agree  with  that  of  the  genus  Selenella,  with  which  genus 
the  external  form  of  the  shell  also  conforms.  In  some  respects  these 
little  shells  have  the  appearance  of  young  individuals;  this  is  especially 
true  in  the  almost  complete  absence  of  concentric  lines  of  growth  and 
in  the  immature  condition  of  the  pscudodeltidium,  the  small  size  is  also 
indicative  of  immaturity,  but  there  is  no  larger  species  of  loop-bearing 
shells  associated  with  this  one  in  the  Louisiana  limestone  fauna,  of  which 
it  might  be  the  immature  representative.  The  specimen  whose  dimen- 
sions have  been  given  above  is  the  largest  one  observed  by  the  writer, 
the  smaller  ones  are  1  mm.  or  less  in  length,  with  all  gradations  between, 
the  specimen  in  which  the  brachidium  has  been  observed  being  one  of 
the  larger  ones. 

Horizon. — Louisiana  limestone. 

Genus  TRIGERIA  Bayle 

Description. — Shell  small,  eentronelliform,  with  subplano-convex  valves, 
marked  with  simple,  radiating  plications.  Internally  the  brachial  valve 
has  an  undivided,  tripartite  hinge-plate,  the  median  division  being  per- 
forated near  the  apex.  The  brachidium  as  in  Centronella  but  with  a 
smaller  anterior  plate. 

Remarks. — The  internal  characters  of  the  single  member  of  this  genus 
here  recognized,  are  not  known,  so  that  it  is  not  possible  to  determine 
whether  or  not  it  is  truly  congeneric  with  Trigeria  guerangeri,  the  genotype. 
It  is,  however,  a  plicated  eentronelliform  shell  and  may  be  retained  in 
this  genus  where  it  was  originally  placed,  until  a  knowledge  of  its  in- 
ternal  characters   shall  prove   that   it   belongs    elsewhere. 

Trigeria  (?)  curriei  Rowley 
Plate  XXX,  Figs.  30-33 

1901.     Trigeria  (?)  curriei  Rowley,  Am.  Geo].,  vol.  27,  p.  350,  pi.  28,  figs 

40-42. 
1P08.     Trigeria  (?)   curriei  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  80,  pi.  17,  figs".  54-56. 

Description.  —  Shell  minute,  plicated,  subovate  in  outline,  longer  than 
wide,  the  greatest  width  near  or  in  front  of  the  middle,  the  anterior  and 
antero-lateral  margins  subsemicircular,  acutely  pointed  posteriorly.  The 
dimensions  of  a  perfect  specimen  are :  length  of  pedicle  valve  2.7  mm., 
length  of  brachial  valve  2.5  mm.,  greatest  width  2.2  mm.,  thickness 
1  mm. 


L;4li  MISSISSIIMMAN   BBACHIOPODA 

Pedicle  valve  subcarinate  along-  the  median  Line,  especially  towards 
the  front,  arched  I  roiti  lieak  to  front  witli  the  curvature  a  little  more 
abrupl  posteriorly,  the  lateral  slopes  gently  convex  from  the  median  line 
to  the  lateral  margins;  the  margins  of  the  valve  between  the  cardinal 
extremities  and  the  apex  of  the  beak  inflected  to  form  a  slight  pseudo- 
cardinal  area  which  lies  in  nearly  the  plane  of  tin,-  valve;  the  beak  prom- 
inent, acutely  pointed,  very  slightly  incurved;  delthyrium  rather  broadly 
triangular,  partially   closed  by  a  pair  of  deltidial  plates  which   do  not 

eo in  contact  along  the  median  line,  thus  leaving  a  triangular  foramen 

which  reaches  from  the  apex  of  the  delthyrium  to  the  base. 

Brachial  valve  less  convex  than  the  pedicle,  with  the  greatest  convexity 
posterior  to  the  middle;  an  angular  or  subangular  median  sinus  originates 
in  or  just  in  front  of  the  umhonal  region  and  continues  to  the  front  margin 
with  increasing  depth,  the  lateral  margins  of  the  sinus  not  defined;  the 
lateral  slopes  of  the  valve  from  the  median  line  to  the  lateral  margins 
of  the  valve  are  transversely  convex  with  the  curvature  a  little  more 
abrupt  towards  the  lateral  margins,  especially  near  the  cardinal  ex- 
tremities; beak  obtusely  pointed,  scarcely  or  not  at  all  incurved. 

Surface  of  both  valves  marked  by  from  eight  to  twelve  rather  broad, 
rounded,  simple  plications  which  originate  in  the  umhonal  region  and  in- 
crease in  strength  .interiorly,  and  by  several  more  or  less  indistinct  lines 
of  growth  which  are  sometimes  nearly  or  quite  obsolete. 

I,' i  marks. — The  internal  characters  of  neither  valve  of  this  species  have 
been  observed,  so  that  the  form  of  brachidium,  if  such  a  structure  be 
present,  is  not  known.  Neither  has  the  punctate  shell  structure  been 
certainly  determined.  In  its  external  features  the  general  form  of  the 
shell  is  notably  centronelloid,  and  being  plicated  it  is  placed  in  the  genus 
Trigeria  where  it  was  first  located  by  Rowley,  the  author  of  the  species. 
The  specimen  whose  dimensions  have  been  given  above  is  perhaps  of 
average  size,  the  larger  examples  attain  a  length  of  4  mm.  or  more. 

Horizon. — Louisiana  limestone. 

Family  TEREBRATULID.E 
Genus  CENTRONELLOIDEA  n.  gen. 

Description. — Shell  small,  centronelliform,  with  smooth  valves,  subovate 
to  subcuneate  in  outline.  Pedicle  valve  with  a  longitudinal  median  ridge 
from  which  the  lateral  surfaces  slope  rather  abruptly  to  the  margins, 
the  beak  acuminate  and  moderately  incurved,  with  a  circular  foramen 
at  the  apex,  the  delthyrium  closed  by  the  pseudodeltidium.  Internally 
the  dental  lamellae  are  well  developed  but  are  of  only  moderate  length. 
The  brachial  valve  much  shallower  than  the  pedicle  with  a  longitudinal 
median  sinus.  Internally  the  hinge  plate  is  divided  medially,  the  two 
lateral  divisions  being  supported  by  a  pair  of  septa  which  rise  from  the 


CENTRONELLOIDEA  247 

floor  of  the  valve  at  either  side  of  the  median  line,  these  septa  continue 
as  crural  lamellae  anteriorly  beyond  the  articulation  of  the  valves  and  their 
inner  margins  are  continued  into  the  crura.    The  brachidium  is  short,  not 

<?  ?  9  9  0  0 

E  F 

Fig.  23. — A  series  of  six  cross-sections  of  the  rostral  portion  of  the  shell  of 
Gentronelloidea  rowleyi  (X  2V2),  showing  the  dental  lamellae  of  the  pedicle 
valve,  and  the  crural  lamellae  of  the  brachial  valve  which  support  the  divided 
hinge-plate,  posteriorly. 

teaching  beyond  the  middle  of  the  shell,  and  like  that  of  Dielasma  in 
form,  but  with  much  less  widely  diverging  primary  lamella1. 

Remarks. — In  its  external  form  this  genus  is  like  Centronella,  but  its 
brachidium  is  essentially  like  that  of  Dielasma,  although  the  development 
of  the  crural  lamellae  in  the  rostral  portion  of  the  brachial  valve  is  entirely 
different  from  that  genus.  The  arrangement  of  these  lamellae  more  nearly 
resembles  the  condition  in  Dielasmoides,  but  the  plates  supporting  the  inner 
margins  of  the  lateral  divisions  of  the  hinge-plate  continue  further 
anteriorly,  forming  a  free  V-shaped  cavity  beyond  the  articulation  of  the 
valves,  and  the  inner  margins  of  the  walls  of  this  cavity  give  origin  to 
the  crura.  The  external  form  of  the  shell  is  entirely  different  from  either 
Dielasma  or  Dielasmoides. 

CENTRONELLOIDEA    ROWLEYI     ( "Worthen  ) 

Plate  XXXI,  Figs.  5-15 

1884.     Terebratula  rowleyi  Worthen,  Bull.  No.  2,  111.  State  Mus  Nat.  Hist , 

p.  23. 
1890.     Terebratula  rowleyi  Worthen,  Geol.  Surv.  111.,  vol.  8,  p.  102,  pi.  11, 

tigs.  6-6b. 
1894.     Terebratula  rowleyi  Keves,  Mo.  Geol.  Surv.,  vol.  5,  p.  105,  pi.  41, 

fig.  23. 
1897.     Dielasma  ?  rowleyi  Sehuchert,  Synop.  Am.  Foss.  Brach.,  p.  213. 

Deseription.  —  Shell  small,  centronelliform,  longer  than  wide,  the  greatest 
width  anterior  to  the  mid-length  of  the  shell,  ovate-subcuneate  in  outline, 
the  postero-lateral  margins  a  little  concave  and  meeting  at  the  beak  in  a 
very  acute  angle,  the  antero-lateral  and  anterior  margins  regularly 
rounded  or  the  anterior  margin  somewhat  truncate.  The  dimensions  of 
two  nearly  perfect  specimens,  metatypes,  are :  length  of  pedicle  valve  10 
mm.  and  9.2  mm.,  length  of  brachial  valve  9  mm.  and  8  mm.,  greatest 
width  7.7  mm.  and  7.8  mm.,  thickness  5  mm.  and  4.8  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  narrowly  rounded 
transversely  across  the  median  line  in  the  posterior  portion,  with  the  lat- 


2  l>  \i  ISSISSIPPIAN    BBACHIOPODA 

era)  slopes  gently  convex  and  dropping  abruptly  to  the  cardinal  extremi- 
ties, anteriorly  the  valve  gradually  becomes  more  broadly  rounded  trans- 
versely with  less  steeply  sloping  sides,  until  at  the  front  ii  is  nearly  regu- 
larly rounded  from  side  to  side;  mesial  sinus  wanting;  the  beak  promi- 
nent, acuminate,  conspicuously  produced  posteriorly  and  not  incurved; 
the  delthyrium  rather  large,  closed  with  a  pseudodeltidium,  the  foramen 
of  moderate  size,  encroaching  upon  the  umbonal  region,  in  contact  with 
tin-  delthyrium  only  at  its  apex. 

Brachial  valve  much  shallower  than  the  pedicle,  conspicuously  sinuate, 
the  sinus  originating  at  the  beak  and  rapidly  broadening  anteriorly  until 
it  occupies  nearly  the  entire  width  of  the  valve  in  front,  the  most  convex 
portions  of  the  valve  are  the  regions  between  the  median  line  and  the 
postero-lateral  margins,  from  which  regions  tlie  surface  curves  rather  ab- 
ruptly to  the  cardinal  extremities  and  less  abruptly  to  the  lateral  margins 
anteriorly;  the  beak  acutely  pointed  and  incurved  beneath  the  margin  of 
the  pseudodeltidium  of  the  opposite  valve. 

Surface  of  both  valves  smooth,  ordinarily  not  even  exhibiting  any  lines 
of  growth;  the  shell  structure  finely  punctate. 

Remarks. — This  species  has  been  incorrectly  identified  by  Hall  and 
<  Jlarke1  and  their  reference  of  it  to  the  genus  Dit  lasma  is  erroneous,  although 
the  specimen  they  have  illustrated  is  a  Dielasma,  and  possibly  D.  formosa. 
The  true  shell  to  which  the  name  Terbratula  rowleyi  was  originally  applied 
is  more  nearly  allied  to  Centrowella  in  external  contour  than  to  Dielasma. 
The  species  is  conspicuously  centronelliform  in  its  external  configuration, 
although  it  is  somewhat  thinner  with  much  less  incurved  pedicle  beak 
than  C.  glans-fagca  the  genotype. 

Horizon. — Burlington  white  chert. 

Genus  CRANMNA  Hall  and  Clarke 

Description. — Shell  terebratuliform.  Pedicle  valve  with  or  without  a 
median  sinus,  and  with  well-developed,  dental  lamellae  of  moderate  length, 
the  foramen  large,  oblique,  and  encroaching  upon  the  umbonal  portion 
of  the  valve,  the  beak  incurved.  Brachial  valve  without  median  fold, 
even  in  those  species  with  a  well-defined  sinus  in  the  opposite  valve,  but 
sometimes  with  a  slight  mesial  depression  near  the  front  margin ;  inter- 
nally the  well-developed  socket  plates  are  connected  transversely  by  a 
concave  hinge-plate  which  is  perforated  at  the  apex  of  the  valve  poste- 
riorly, upon  the  inner  or  concave  surface  of  the  hinge-plate  a  pair  of 
ridges  originate  at  or  near  the  anterior  margin  of  the  perforation  and  con- 
tinue anteriorly  across  the  plate  from  the  front  of  which  they  are  pro- 
duced into  the  crura,  these  crural  ridges  upon  the  hinge-plate  divide  that 

i  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81,  figs.  27-28.    (1894.) 


CRAN^ENA 


249 


plate  into  three  subequal  parts  or  into  two  equal  lateral  divisions  and  a 
broader  central  one,  and  in  some  species  the  crural  ridges  are  accom- 
panied by  similar  ridge-like  thickenings  upon  the  opposite  side  of  the 
hinge-plate.  The  brachidium  is  short  and  Dielasma-like,  not  reaching  to 
the  middle  of  the  valve. 


<0> 


B  C 


t^r 


Fig.  24. — A  series  of  ten  cross-sections  of  the  rostral  portion  of  the  shell  of 
Cranwna  iowensis  (X  21/£),  only  one  of  which  (A)  shows  the  pedicle  valve 
with  the  dental  lamellae.  In  the  brachial  valve  is  shown  the  concave  hinge- 
plate,  perforated  posteriorly,  with  the  crural  ridges  passing  anteriorly  into 
the  crura. 

Remarks.  —  This  genus  differs  fundamentally  from  Dielasma  in  the 
origin  of  the  crura  from  the  thickened  crural  ridges  of  the  hinge-plate, 
rather  than  from  the  crural  lamella?  resting  upon  the  inner  surface  of  the 
valve,  and  in  the  absence  of  a  special  plate  in  the  brachial  valve  for  mus- 
cular attachment,  the  muscles  being  attached  directly  to  the  inner  surface 
of  the  valve.  From  Girtyella  the  genus  may  be  distinguished  by  the  ab- 
sence of  a  median  septum  in  the  brachial  valve  and  by  the  origin  of  the 
crura  from  crural  ridges  on  the  hinge-plate  rather  than  from  the  anterior 
extension  of  the  inner  extremities  of  the  socket  plates. 

Craklena  globosa  n.  sp. 
Plate  XXXIV,  Pigs.  60-66 

1895.     Dielasma  Burlingtonensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  81,  figs.  9-11. 
1895.     Dielasma  formosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 

figs.  14-15  (not  figs.  12-13.  16-26). 

I>t  scription.— Shell  small,  subovate  in  outline,  longer  than  wide,  the 
greatest  width  near  the  mid-length,  the  valves  subequally  convex.  The 
dimensions  of  two  complete  examples  are:  length  of  pedicle  valve  14  mm. 
and  10.5  mm.,  length  of  brachial  valve  12  mm.  and  9.1  mm.,  greatest  width 
10.3  mm.  and  8  mm.,  thickness  9.4  mm.  and  5.8  mm. 


250  MISSISSII'I'IAN    BRACHIOPODA 

Pedicle  valve  strongly  convex,  the  greatesl  convexity  posterior  to  the 
middle,  arched  from  beak  to  front  along  the  median  line  with  the  curva- 
ture becoming  regularly  more  convex  posteriory,  the  surface  curving  ab- 
ruptly from  the  median  line  towards  the  postero-lateral  margins  and  be- 
coming inflected  towards  (lie  cardinal  extremities,  curving  more  gently  to 
the  anterolateral  and  anterior  margins;  mesial  sinus  obsolete  and  the 
mesial  portion  of  the  valve  not  differentiated  from  the  lateral  slopes;  the 
beak  prominent,  incurved,  pierced  by  a  subcircular  foramen  which  en- 
croaches wholly  upon  the  nmhonal  portion  of  the  valve,  only  coining  in 
contact  with  the  dcllhyrium  at  its  apex  ;  delthyrium  largely  occupied  by 
tl"'  incurved  beat  of  the  opposite  valve,  the  remaining  space  closed  by 
the  deltidial  plates.  Internally  the  dental  plates  are  well  developed  and 
extend  anteriorly  from  the  beak  for  nearly  one-fourth  the  length  of  the 
valve;  the  muscular  scars  obscure  or  obsolete  in  smaller  specimens,  but 

Fig.  25. — A  series  of  six  cross-sections  of  the  rostral  portion  of  the  brachial  valve 
of  Cranwna  globosa  (X  2%),  showing  the  concave  hinge-plate  which  is  per- 
forated posteriorly,  and  the  crural  ridges  upon  the  hinge-plate. 

on  the  internal  casts  of  larger  and  older  examples  they  are  suggested  by 
more  or  less  indefinite  markings  radiating  from  the  beak. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  convex- 
ity near  the  middle,  the  surface  regularly  arched  from  beak  to  front 
along  the  median  line  with  the  curvature  a  little  more  convex  posteriorly, 
from  the  mesial  line  the  surface  is  rather  abruptly  curved  to  the  postero- 
lateral margins  and  somewhat  more  gently  to  the  antero-lateral,  and  an- 
terior margins ;  the  mesial  portion  of  the  valve  not  differentiated  from 
the  lateral  slopes ;  beak  acutely  pointed,  incurved  beneath  the  base  of  the 
pseudodeltidium  of  the  opposite  valve.  Internally  the  socket  plates  are 
joined  transversely  by  an  elongate,  concave  hinge-plate  which  is  perfor- 
ated at  its  apex,  anteriorly  beyond  the  articulation  of  the  valves  the 
lateral  attachments  of  the  hinge-plate  to  the  inner  surface  of  the  shell 
retreat  from  the  lateral  margins  of  the  valve  and  these  continuations  of  the 
socket  plates  are  reduced  to  mere  ridges  between  which,  upon  the  con- 
cave side  of  the  hinge-plate,  a  pair  of  crural  ridges  originate ;  the  crural 
ridges  diverge  anteriorly  and  are  produced  into  the  bases  of  the  crura, 
they  are  still  connected  transversely  by  the  anterior  extremity  of  the 
hinge-plate  after  connections  with  the  inner,  lateral  surfaces  of  the  valve 
have  disappeared;  the  brachidium  is  short  and  Dielasma-like  with  rather 
widely  divergent  descending  lamella^  and  sharply  recurved  ascending 
lamella?. 


CRAN-aSNA  251 

Surface  of  both  valves  marked  only  by  concentric  lines  of  growth  which 
vary  in  the  strength  of  their  development.  Shell  structure  finely  and 
closely  punctate. 

Remarks. — This  is  a  small  species  and  may  be  easily  recognized  by  its 
more  or  less  rotund  form  and  by  the  absence  of  fold  or  sinus.  Specimens 
of  it  have  sometimes  been  identified  as  Dielasma  formosa,  but  besides  being 
entirely  different  from  Dielasma  in  the  essential  characters  of  the  interior 
of  the  rostral  portion  of  the  brachial  valve,  it  is  a  comparatively  broader 
shell  with  the  valves  more  regularly  arched  transversely.  The  species 
shows  considerable  variation  in  outline,  especially  in  the  position  of  the 
line  of  greatest  width,  it  being  sometimes  anterior  and  sometimes  poste- 
rior to  the  mid-length  ;  it  also  varies  in  the  convexity  of  the  valves,  in 
some  old  individuals  becoming  ventricose.  The  species  never  attains  a 
great  size,  about  17  mm.  being  the  maximum  length  which  has  been 
observed. 

Horizon. — Burlington  limestone. 

Cran/Ena  sulcata  n.  sp. 

Plate  XXXIV,  Figs.  55-59 

1895.     Dielasma  turgida  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 
figs.  1-3  (not  figs.  4-8). 

Description.  —  Shell  small,  ovate,  subpentagonal  in  outline,  the  anterior 
margin  emarginate,  longer  than  wide,  the  greatest  width  near  the  mid- 
length  of  the  shell.  The  dimensions  of  a  nearly  perfect  individual  are : 
length  of  pedicle  valve  11  mm.,  length  of  brachial  valve  9.2  mm.,  greatest 
width  8.8  mm.,  thickness  8.1  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  near  or  posterior 
to  the  middle,  the  surface  almost  regularly  arched  from  the  beak  to  the 
front  or  with  the  curvature  a  little  more  convex  posteriorly,  the  surface 
curving  abruptly  to  the  lateral  margins  becoming  inflected  to  the  cardinal 
extremities;  mesial  sinus  originating  near  the  middle  of  the  valve,  rather 
narrow  or  of  moderate  width,  rounded  in  the  bottom,  sometimes  becoming 
deep  at  the  anterior  margin,  its  lateral  margins  rounding  into  the  lateral 
slopes  of  the  valve  without  sharp  demarcation ;  the  beak  pointed,  rather 
strongly  incurved,  perforated  by  a  subcircular  foramen  which  encroaches 
wholly  upon  the  umbonal  region,  coming  in  contact  with  the  delthyrium 
only  at  its  apex ;  delthyrium  broadly  triangular,  closed  by  deltidial  plates 
throughout,  except  as  it  is  filled  with  the  beak  of  the  opposite  valve.  In- 
ternally the  dental  lamella?  are  well  developed  and  of  moderate  length. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  the  surface  arched  from  beak  to  front  along  the 
median  line  with  the  curvature  sometimes  more  abrupt  posteriorly  and 
sometimes  anteriorly,  the  curvature  to  the  lateral  margins  rather  abrupt; 


252  \i  ISSISSII'I'IAX    BBACHIOPODA 

the  mediae  portion  of  the  valve  undifferentiated  from  the  general  convex- 
ity of  the  valve  or  rather  indefinitely  flattened  towards  the  front,  never 
depressed  in  a  mesial  sinus  or  elevated  in  a  fold;  beak  prominent  and 
incurved  beneath  that  of  the  opposite  valve.  Internally  the  socket  plates 
are  joined  transversely  by  an  elongate,  concave  hinge-plate  which  is  per- 
forated at   the  apex,  anteriorly  the  sockel   plates  are  reduced  and  the  lat- 


A 


8  e  D  E 


\^ 


vy 


Fig.  26. — A  series  of  ten  cross-sections  or  the  rostral  portion  of  the  shell  of 
Crana  mi  sulcata  (X  2V2),  showing  the  hinge-plate  perforated  posteriorly,  and 
the  crural  ridges. 

era!  attachments  of  the  hinge-plate  to  the  inner  surface  of  the  valve  re- 
heat from  the  Lateral  margins,  a  pair  of  ridges  diverge  anteriorly  from 
near  the  apex  upon  the  concave  surface  of  the  hinge-plate,  which  become 
the  bases  of  the  crura,  the  concave  hinge-plate  continues  to  join  the  crural 
bases  after  their  lateral  connection  with  the  inner  surface  of  the  valve  has 
Income  discontinued;  complete  brachidium  not  known,  but  it  is  believed 
to  be  short  and  Dielasma-like  in  form. 

Remarks. — This  species  has  commonly  been  identified  with  the  form  here 
defined  as  GirtyeUa  hin/i<hi,  but  it  is  a  larger  species  besides  being  totally 
different  from  that  one  in  the  apical  portion  of  the  interior  of  the  brachial 
valve;  it  differs  externally  from  that  species  in  the  absence  of  a  mesial 
sinus  in  the  brachial  valve  and  in  having  the  beak  of  the  pedicle  valve  a 
little  less  incurved.  The  species  resembles  Dielasma  simiata  externally,  but 
it  is  much  smaller  and  the  different  mode  of  attachment  of  the  crural 
plates  in  the  apex  of  the  brachial  valve  is  a  character  of  generic  value. 

Horizon.  —  Salem  limestone. 

CraN/Ena  (?)  allei  (Winchell) 
Plate  XXXIV,  Fig.  51 

1865.     Centronella  Allei  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  123. 
1901.     Dielasma  allei  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11,  pp.  162 
and  189,  pi.  14,  fig.  10. 

Description. — Shell  small,  subovate  or  ovate-subpentagonal  in  outline, 
the  anterior  margin  rounded,  the  greatest  width  near  the  mid-length. 
The  dimensions  of  a  pedicle  valve  are :  length  10.5  mm.,  width  9  mm., 
convexity  2.5  mm.  The  dimensions  of  a  brachial  valve  are:  length  9 
mm.,  width  8.8  mm.,  convexity  2  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  moderately  convex  in  the  umbonal  region  and  rather  abruptly 


DIELASMOIDES  253 

inflected  towards  the  cardinal  extremities,  gently  convex  to  the  antero- 
lateral and  anterior  margins;  mesial  sinus  obsolete;  the  beak  a  little  flat- 
tened, incurved,  pierced  by  a  rather  large  foramen  which  encroaches  upon 
the  umbonal  region.  Internally  the  dental  lamellae  are  well  developed  and 
of  moderate  length. 

Brachial  valve  subequally  convex  with  the  pedicle,  its  greatest  con- 
vexity near  or  posterior  to  the  middle,  the  surface  curving  more  abruptly 
to  the  postero-lateral  margins  and  gently  to  the  antero-lateral  and  an- 
terior margins;  neither  mesial  fold  nor  sinus  present;  the  beak  pointed, 
incurved  beneath  that  of  the  opposite  valve.  Internal  characters  not 
determined. 

Remarks. — In  the  preparation  of  the  original  description  of  this  species 
Winched  probably  had  two  or  more  different  forms  in  hand.  The  type 
specimens  are  said  to  have  come  from  the  upper  "Yellow  sandstone"  and 
the  "Oolite  bed"  of  the  Kinderhook  at  Burlington,  Iowa,  and  it  is  said 
also  to  occur  at  Hamburg,  Illinois,  and  Talmadge,  Ohio.  In  the  original 
definition  a  specimen  from  the  upper  yellow  sandstone  was  used  as  the 
basis  for  the  description  of  the  pedicle  valve,  and  specimens  from  the 
oolite  were  used  for  the  description  of  the  brachial  valve  and  the  shell 
structure.  It  is  probable  that  these  specimens  belong  to  two  different 
forms,  and  the  form  from  the  yellow  sandstone  will  here  be  considered 
as  the  type  of  the  species.  The  true  generic  characters  of  this  yellow  sand- 
stone species  has  not  been  determined,  and  cannot  be  in  the  condition 
of  preservation  in  which  specimens  have  been  found.  It  can  be  clearly 
seen,  however,  that  they  do  not  possess  a  median  septum  in  the  brachial 
valve  and  therefore  cannot  belong  to  the  genus  Girtyella,  neither  do  they 
have  the  crural  lamellae  resting  upon  the  inner  surface  of  the  valve  as  in 
Diclasma,  and  the  species  can  therefore  be  excluded  from  that  genus.  The 
specimens  from  the  Hamburg,  Illinois,  locality  are  certainly  examples  of 
the  shell  which  has  here  been  defined  as  Hamburgia  typa,  and  while  the 
yellow  sandstone  specimens  are  certainly  specifically  different  from  these 
Hamburg  shells,  it  is  still  possible  that  they  belong  to  the  same  genus. 
The  species  is  referred  to  Cranc&na,  however,  because  on  the  whole  its  mem- 
bers seem  more  closely  to  resemble  other  species  of  that  genus  than 
anything  else. 

He  rizon.—  Kinderhook. 

Genus  DIELASMOIDES  Weller 

Description. — Shell  terebratuliform.  Pedicle  valve  bisinuate  towards 
the  front  in  the  genotype,  the  two  depressions  separated  by  a  low,  broadly 
rounded  mesial  elevation;  the  dental  lamellae  well  developed  internally; 
the  foramen  large,  oblique,  encroaching  wholly  upon  the  umbonal  region. 
Brachial  valve  with   a  slight   mesial  flattening  or  depression  anteriorly 


254  MISSISSEPPIAN    BRACHIOPODA 

in  the  genotype;  internally  the  socket  plates  are  supported  at  their  inner 
margins  by  a  pair  of  lamella'  which  pass  obliquely  towards  the  floor  of  the 
valve  to  which  they  are  joined  near  the  median  line,  between  these 
lanielhe,  the  outer  walls  of  the  valve,  and  the  socket  plates,  are  a  pair 
of  cavities  narrowly  triangular  in  cross-section,  which  expand  anteriorly 
and  open  out  into  the  general  cavity  of  the  valve;  the  crura  originate 
from  the  anterior  extension  of  the  inner  walls  of  the  socket  plates. 

°  ^  O  ^  ^  ^>  KS 

C  D 

I'm.  27. — A  series  of  seven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Dielasmoides  bisinuata  (X  2y2),  showing  the  dental  lamellae  of  the  pedicle 
valve,  and  the  lamellae  supporting  the  hinge-plate  in  the  brachial  valve. 

lit  marks. —  In  the  presence  of  the  triangular  cavities  in  the  apical 
portion  of  the  brachial  valve  this  genus  resemhles  Diclasma,  but  in  this 
ease  the  outer  hounding  walls  of  the  cavities  are  the  socket  plates  rather 
than  the  basal  portions  of  the  special  crural  lamellae,  and  the  crura  are  an- 
terior extensions  from  the  inner  walls  of  the  sockets  instead  of  arising  as 
separate  crural  lamella'  originating  at  the  apex  of  the  valve.  The  special, 
transverse,  muscle-bearing  plate  is  also  absent  in  this  genus.  The  genus 
is  perhaps  to  be  compared  with  Girtyella  as  the  form  to  which  it  is  most 
closely  allied.  As  in  Girtyella  the  crura  originate  from  the  inner  walls 
of  the  sockets,  hut  the  hinge-plate  supported  by  a  median  septum  is 
wanting.  The  supporting  lamella?  of  the  socket-plates,  however,  may  be 
considered  as  a  hinge-plate  .similar  to  that  of  Girtyella,  which  has  become 
so  deeply  concave  that  it  rests  upon  and  is  coalescent  with  the  outer  wall 
of  the  valve  at  and  on  either  side  of  the  median  line.  This  arrangement 
of  the  lamella?  in  the  rostral  portion  of  the  brachial  valve  is  considered 
as  the  essential  generic  character  of  the  group ;  whether  the  bisinuate 
configuration  of  the  pedicle  valve  is  also  of  generic  value  can  not  be 
determined  from  the  single  species  of  the  genus  so  far  recognized. 

Dielasmoides  bisinuata  Weller 

Plate  XXXI,  Figs.  19-24 

1911.     Dielasmoides  bisinuata  Weller,  Jour.  Geol.,  vol.  19,  p.  443,  figs.  3a-g 

Description.  —  Shell  below  medium  size,  ovate  in  outline,  the  greatest 
width  anterior  to  the  mid-length,  the  anterior  margin  rounded.  The 
dimensions  of  two  nearly  complete  specimens  are :  length  of  pedicle 
valve  20.5  mm.  and  16.3  mm.,  length  of  brachial  valve  18.9  mm.  and  14..° 
mm.,  greatest  width  14.3  mm.  and  12.8  mm.,  thickness  8.6  mm.  and  8  mm. 


DIELASMOIDES 


255 


Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  convexly  curved  from  front  to  beak  with  the  curvature 
progressively  greater  posteriorly,  the  surface  only  gently  convex  trans- 
versely in  the  posterior  two-thirds  of  the  valve,  except  towards  the 
postero-lateral  margins  where  it  is  abruptly  curved  towards  the  opposite 
valve  and  becomes  inflected  towards  the  cardinal  exti'emities ;  towards 
the  front  of  the  valve,  about  one-third  of  its  length  from  the  anterior 
margin,  two  shallow,  broadly  rounded,  longitudinal  depressions  or  sinuses 
originate,  which  lie  symmetrically  on  each  side  of  a  low,  broadly  rounded 
mesial  fold  which,  however,  does  not  rise  above  the  general  surface  of 
the  valve  outside  the  longitudinal  sinuses;  the  beak  strongly  incurved 
so  that  the  delthyrium  is  entirely  hidden  by  the  contact  with  the  opposite 
valve,  the  foramen  large  and  encroaching  wholly  upon  the  umbonal 
portion  of  the  valve.  Internally  the  dental  plates  are  well  developed  and 
extend  anteriorly  from  the  beak  for  about  one-sixth  or  one-fifth  the 
length  of  the  valve. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  curvature  of  the  surface  along  the 
median  line  is  gently  convex  with  the  curvature  more  abrupt  posteriorly, 
transversely  the  surface  is  somewhat  narrowly  rounded  in  the  mesial 
portion  and  then  slopes  with  a  gently  convex  curvature  to  the  lateral 
margins,  the  curvature  becoming  more  abrupt  posteriorly ;  mesial  portion 
of  the  valve  in  its  anterior  one-fourth,  depressed  in  a  short,  rather  broad 
and  shallow  mesial  sinus,  the  bounding  folds  on  either  side  scarcely 
differentiated  from  the  general  curvature  of  the  valve ;  the  beak  pointed 
and  incurved  beneath  that  of  the  opposite  valve.  Internally,  the  socket 
plates  lie  in  nearly  the  plane  of  the  valve  posteriorly,  and  are  supported 
at  their  inner  margins  by  a  pair  of  lamelke  which  extend  obliquely  to 
the  floor  of  the  valve  to  which  they  are  joined  on  either  side  of  the 
median  line,  the  crural  bases  being  an  anterior  extension  of  the  inner 
edges  of  the  socket  plates;  median  septum  absent. 

Remarks. — This  species  is  peculiar  among  our  loop-bearing  shells  in 
having  the  bisinuate  configuration  of  the  pedicle  valve  towards  the  front, 
and  the  short  median  sinus  in  the  brachial  valve.  This  configuration  is 
sometimes  obscure,  especially  in  smaller  or  immature  shells,  but  in  full 
grown  specimens  it  is  probably  always  present  in  some  degree,  although 
more  pronounced  in  some  individuals  than  in  others.  In  its  general  form, 
aside  from  its  bisinuate  configuration,  the  species  most  closely  resembles 
some  species  of  Dielasma,  especially  such  a  species  as  D.  su~bspatulata, 
although  the  greatest  width  of  the  shell  is  not  so  far  forward  as  in  that 
species. 

Locality.—  Patrick's  Quarry,  Middle  Fabius  river,  Lewis  Co..  Mo. 


2")(i  MIssissil'l'lAN    BBACHIOPODA 

Genua  DIELASMA  King 

Description, — Shell  terebratuliform.  Pedicle  valve  with  or  without  a 
median  sinus,  and  wiili  well-developed  dental  lamellae  internally,  the 
foramen  Large  and  encroaching  upon  the  umbonal  portion  of  the  valve, 
the  beak  strongly  incurved.  Brachial  valve  usually  without  mesial  fold; 
internally  the  crural  plates  are  separate  from  the  denial  socket  plates, 
they  diverge  from  the  apex  of  the  valve  with  an  elongate  attachment  to 
the  inner  surface  of  the  valve,  the  free  portion  of  the  brachidium  is 
short  with  diverging  descending  lamella?;  between  the  crural  plates  for 
the  full  Length  of  their  attachment  to  the  inner  surface  of  the  valve,  is 
a  concave,  transverse  plate  Tor  museular  attachment,  which  joins  the 
inner  surface  of  the  crural  plates  a  little  above  their  bases,  this  plate  rests 
against  the  inner  surface  of  the  valve  along  the  median  line  for  a  portion 
or  the  whole  of  its   length,  or  may  he   free  throughout,  when' attached 

y    Y    y    v    ^    w    \^y 

^y    \&/     \J±s  '  \n 

y  v 


Pig.  28. — A  series  of  fourteen  cross-sections  of  the  rostral  portion  of  the  brachial 
valve  of  Dielasma  formosavi  (X  2V&),  showing  the  development  of  the  crural 
lamellae  entirely  independent  from  the  hinge-plate,  and  the  transverse,  muscle- 
bearing  plate  between  them. 

along  the  median  line  a  pair  of  slender  cavities,  triangular  in  cross  section, 
converge  from  the  general  cavity  of  the  shell  towards  the  beak;  when  the 
transverse  plate  is  not  attached  along  its  median  line  there  is  a  single, 
broad  and  low  cavity  beneath  the  plate  extending  towards  the  apex, 
anteriorly  this  plate  extends  to  a  greater  or  less  distance  beyond  the 
attachment  of  the  crural  plates  and  is  pointed,  rounded  or  emarginate  in 
front,  its  surface  is  marked  by  concentric  wrinkles  parallel  with  its  an- 
terior margin  which  are  usually  discontinuous  along  the  median  line. 

Remarks. — The  genus  Dielasma  was  established  by  King  with  Terebratula 
dongatus  Schl.  as  genotype,  and  although  he  defined  the  genus  primarily 
upon  the  presence  of  prominent  dental  lamella^  in  the  pedicle  valve  and 
on  the  form  of  the  loop,  his  illustrations  of  the  internal  casts  of  the  species 
under  the  name  Epithyris  eiongata1  show  that  the  crural  plates  are  separate 
from  the  socket  walls,  one  of  the  most  essential  features  of  Dielasma  a.s 
here  defined.     Davidson2  gives    illustrations    of  the  same  species  which 

lMon.  Permian  Foss.  Eng.,  pi.  6,  figs.  37,  41.     (1850.) 

2  Brit.  Foss.  Brach.,  vol.  2,  Permian,  pi.  1,  figs.  18,  20.     (1857.) 


DIELASMA  257 

exhibit  all  the  essential  generic  characters  of  Dielasma  must  perfectly. 
The  interpretation  of  the  genus  by  Hall  and  Clarke1  is  identical  with 
that  here  given,  but  those  authors  included  certain  species  in  the  genus 
without  sufficient  investigation  of  their  internal  characters,  which  are 
really  fundamentally  different ;  it  has  in  fact  been  the  usual  custom 
among  American  workers,  since  the  publication  of  Hall  and  Clarke's 
work,  to  refer  all  Mississippian  terebratuloid  shells  to  the  genus  Dielasma. 
In  specimens  preserved  in  the  condition  of  internal  casts  the  generic 
characters  of  Dielasma  are  always  very  obvious,  the  position  of  crural 
lamella1,  separate  from  the  socket  plates  being  indicated  by  a  pair  of 
slits  diverging  from  the  beak  of  the  brachial  valve ;  when  the  transverse 
muscle-bearing  plate  is  attached  along  its  mesial  line  a  second  pair  of 
diverging  slits  are  present  between  those  formed  by  the  crural  lamellae 
and  the  finger-like  casts  of  the  slender  cavities  beneath  the  transverse 
plate  are  clearly  shown,  whether  they  are  actually  present  or  broken  off. 
In  specimens  having  the  shell  preserved  the  shell  substance  is  frequently 
translucent  enough  to  show  the  position  of  the  internal  lamella?  as  dark 
lines,  in  which  case  the  genus  can  be  recognized  at  once,  and  when  the 
shell  is  opaque  it  is  usually  easy  to  determine  the  generic  characters  by 
the  judicious  use  of  a  needle,  without  injuring  the  specimen  as  to  its 
external  form  and  characters  upon  which  the  various  species  are  dif- 
ferentiated. 

Dielasma  chouteauensis  n.  sp. 

Plate  XXXII,  Figs.  1-17 

1895.     Dielasma  formosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 
fig.  24  (not  figs  12-23,  25-26). 

Description.  —  Shell  of  medium  size  or  larger,  subovate  or  obscurely 
subpentagonal  in  outline,  the  greatest  width  near  the  middle,  the  anterior 
margin  rounded.  The  dimensions  of  a  nearly  complete  example  are : 
length  of  pedicle  valve  32  mm.,  length  of  brachial  valve  29.3  mm.,  greatest 
width  23.2  mm.,  thickness  ±15  mm.  . 

Pedicle  valve  most  convex  posterior  to  the  middle,  arched  from  beak 
to  front  along  the  median  line  with  the  curvature  becoming  progressively 
greater  posteriorly,  the  surface  convexly  curved  from  the  median  line 
towards  the  postero-lateral  margins  for  a  little  more  than  half  way  to  the 
margins  where  it  is  rather  abruptly  inflected  to  a  slight  degree,  along  a 
narrowly  rounded,  arched  ridge  which  originates  at  the  side  of  the  beak 
and  terminates  at  the  lateral  margin  posterior  to  the  middle  of  the  valve, 
beyond  this  arched  ridge  the  inflected  surface  is  usually  gently  concave, 
to  the  lateral,  antero-lateral  and  anterior  margins  the  surface  is  gently 
convex;  the  mesial  portion  of  the  valve  is  usually  slightly  flattened  be- 

lPal.  N.  Y.,  vol.  8,  pt.  2,  pp.  293-294.     (1894.) 
—9 


258  M  ississil'l'IAN    BRACHIOPODA 

tween  ill-defined  lines.  hut  is  not  depressed  in  a  median  sinus;  the  beak 
prominent,  pointed  and  incurved,  pierced  by  a  large,  subovate  foramen 
which  encroaches  upon  the  umbonal  region,  only  coining  in  contact  with 
the  delthyrium  al  its  apex;  the  delthyrium  almost  totally  hidden  by  the 
incurvature  of  the  beak.    Internally  the  dental  lamella-  are  well  developed 


Q 


u     \jf     i~j     \^j 

B  c  O  E 

w     w    w 


Fig.  29. — A  series  of  ten  cross-sections  of  the  rostral  portion  of  the  shell  of 
Dielasma  chouteauensis  (X  2VL>)>  showing  the  dental  lamellae  of  the  pedicle 
valve  (A),  and  the  development  of  the  independent  crural  lamella?  of  the 
brachial  valve,  with  a  transverse,  muscle-bearing  plate  which  becomes  entirely 
free  from  the  floor  of  the  valve  anteriorly. 

and  reach  nearly  one-fourth  the  length  of  the  valve  from  the  beak;  the 
muscular  scars  obscure,  bounded  laterally  by  a  pair  of  shallow,  narrow, 
rounded  furrows  in  the  inner  sin  face  of  the  valve  which  diverge  from 
the  beak  between  the  dental  lamella'  and  extend  about  two-thirds  the 
length  of  the  valve  from  the  beak. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  arched  from  beak  to  front  with  the  greater 
curvature  posteriorly,  the  surface  curving  abruptly  to  the  postero- 
lateral margins  and  gently  to  the  anterior  and  antero-lateral  margins ; 
the  median  portion  of  the  valve  not  differentiated  as  a  fold  or  sinus  and 
scarcely  even  flattened;  the  beak  acutely  pointed,  incurved  beneath  that 
of  the  opposite  valve.  Internally  the  socket  plates  are  distinct  from  the 
crural  plates ;  the  crural  plates  originate  as  a  pair  of  slight  angular  ridges 
diverging  from  the  apex  upon  the  inner  surface  of  the  valve;  between 
these  ridges  is  a  concave  platform-like  area  for  muscular  attachment 
which  is  at  first  wholly  confluent  with  the  inner  surface  of  the  valve, 
anteriorly  it  becomes  elevated  a  little  above  the  floor  of  the  valve  laterally, 
leaving  a  narrow,  triangular,  pocket-like  cavity  on  each  side,  still  further 
towards  the  front  this  platform  is  elevated  above  the  inner  surface  of 
the  valve  through  its  entire  width,  leaving  a  broad,  shallow  cavity  be- 
tween its  under  surface  and  the  inner  surface  of  the  valve,  the  anterior 
extremity  reaching  one-third  or  more  of  the  length  of  the  valve  from 
the  apex. 

Surface  of  both  valves,  at  least  in  Avell  preserved  exfoliated  examples, 
marked  towards  the  lateral  and  anterior  margins  by  exceedingly  faint. 


DIELASMA  259 

depressed,  radiating  costffi,  about  three  of  which  occupy  the  space  of  one 
millimeter;  the  concentric  lines  of  growth  are  more  or  less  obscure  in 
smaller  individuals,  becoming  somewhat  stronger  and  more  crowded 
towards  the  outer  margin  of  large  individuals.  Shell  structure  finely 
and  closely  punctate. 

Hi  marks. — This  species  is  rather  common  in  the  Chouteau  limestone 
of  central  Missouri.  Hall  and  Clarke  illustrated  a  large,  typical  example 
of  the  species  as  Dielasma  formosa,  but  it  may  be  easily  distinguished  from 
that  species  by  the  more  depressed  convex  valves  which  are  much  more 
regularly  convex  transversely.  Internally  the  two  species  are  also  dis- 
tinct, though  both  possess  the  essential  characters  of  Dielasma;  in  D. 
chouteauensis  the  muscular  platform  of  the  brachial  valve  becomes  elevated 
free  from  the  inner  surface  of  the  valve  anteriorly,  while  in  D.  formosa 
the  median  contact  is  retained  throughout.  The  fine,  radiating  costs3  have 
been  observed  on  only  a  few  examples ;  it  is  possible  that  they  were 
uniformly  present  upon  the  living  shells,  but  have  usually  been  obliterated 
in  the  fossils  by  exfoliation  since  all  the  known  examples  occur  in  that 
condition. 

Horizon.— Chouteau  limestone. 

Dielasma  fernglenensis  Weller 
Plate  XXXIII,  Figs.  1-5 
1909.     Dielasma  fernglenensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  318, 
pi.  14,  fig.  7. 

Description. — Shell  large,  subovate  in  outline,  longer  than  wide,  the 
greatest  width  a  little  anterior  to  the  middle.  The  dimensions  of  the 
type  specimen,  as  nearly  as  can  be  determined,  are :  length  of  pedicle 
valve  55  mm.,  length  of  brachial  valve  51.4  mm.,  width  — 43  mm.,  thick- 
ness ±25  mm. 

Pedicle  valve  moderately  convex,  the  curvature  greatest  towards  the 
postero-lateral  margins,  becoming  inflected  towards  the  cardinal  extrem- 
ities ;  mesial  portion  of  the  valve  not  differentiated  from  the  general  curv- 
ature of  the  surface ;  beak  pointed  and  closely  incurved,  pierced  by  a  large 
foramen  which  encroaches  wholly  upon  the  umbonal  portion  of  the  valve, 
the  deltidial  plates  hidden  by  the  incurvature  of  the  beak.  Internally  the 
dental  lamellae  well  developed  and  of  moderate  length. 

Brachial  valve  probably  about  equally  convex  with  the  pedicle,  the 
curvature  strongest  towards  the  postero-lateral  margins,  rather  gentle  to 
the  antero-lateral  and  anterior  margins ;  mesial  portion  of  the  valve  not 
differentiated  from  the  general  curvature  of  the  surface ;  beak  pointed  and 
inemwed  beneath  the  pseudodeltidium  of  the  opposite  valve.  Internally 
the  crural  lamella1  diverge  from  the  beak  and  are  separate  from  the  socket 
plates,  being  joined  transversely  by  a  concave,  muscle-bearing  plate  as  in 


260  M  ississil'i'i an    BBACHIOPODA 

all  members  of  the  genus  Dielasma,  but  the  details  of  these  structures  can- 
not be  determined  in  the  type  specimen. 

Surface  of  the  valves  apparently  nearly  smooth  except  towards  the 
outer  margin  where  there  are  several  concentric  lines  of  growth  varying 
in  strength.    The  shell  structure  is  finely  and  closely  punctate. 

Remarks. — This  species  resembles  D.  chouteauensis,  but  it  is  propor- 
tionally broader,  and  has  the  transverse,  muscle-bearing  plate,  between 
the  hascs  of  the  crural  lamella1,  attached  to  the  floor  of  the  valve  through 
the  whole,  or  nearly  the  whole,  of  its  Length. 

Horizon. —  Fern  (lien  formation. 

Dielasma  osceolensis  q.  sp. 
Plate  XXXI II,  Figs.  1-3 

Descript ion. — Shell  large,  elongate-subovate  in  outline,  the  anterior 
margin  rounded,  the  greatest  width  near  the  mid-length.  The  dimensions 
of  a  very  complete  hut  slightly  distorted  example,  the  holotype,  are: 
length  of  pedicle  valve  52  mm.,  length  of  brachial  valve  48  mm.,  greatest 
width  32.4  mm.,  thickness  22.8  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  arcuate  from  beak  to  front  with  the  curvature 
increasingly  convex  posteriorly,  curving  rather  abruptly  towards  the 
postero-lateral  margins,  becoming  incurved  to  the  cardinal  extremities, 
the  curvature  to  the  antero-lateral  and  anterior  margins  more  gentle; 
mesial  sinus  obsolete  but  the  mesial  portion  of  the  valve  is  obscurely  flat- 
tened ;  the  beak  prominent,  pointed,  strongly  incurved,  the  deltidial  plates 
nearly  hidden  by  the  incurvature,  the  foramen  very  large,  elongate-ovate, 
encroaching  wholly  upon  the  umbo.  Internally  the  dental  plates  are 
strongly  developed  and  elongate,  reaching  anteriorly  from  the  beak  nearly 
one-fourth  the  length  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  surface  curving  more  abruptly  to  the 
postero-lateral  margins  and  somewhat  gently  to  the  antero-lateral  and 
anterior  margins ;  mesial  portion  of  the  valve  obscurely  flattened  but  not 
differentiated  from  the  general  convexity ;  the  beak  pointed  and  incurved 
beneath  that  of  the  opposite  valve.  Internally  the  crural  lamella1  are 
separate  from  the  socket  plates  and  diverge  anteriorly  from  the  beak, 
extending  about  one-fifth  the  length  of  the  valve ;  entire  braehidium  not 
observed. 

Surface  of  both  valves  marked  only  by  concentric  lines  of  growth  which 
are  obscure  posteriorly,  becoming  stronger  and  wrinkle-like  towards  the 
front.     Shell  substance  finely  punctate. 

Remarks. — This  species  is  one  of  the  largest  in  our  faunas  and  resembles 
some  European  specimens  which  have  been  identified  as  Tcrrbrahila  hastata, 


DIELASMA  261 

it  differs  from  the  original  illustration  of  that  species,  however,  in  the 
absence  of  a  mesial  sinus  in  each  valve.  It  more  closely  resembles 
D.  chouteauensis  or  D.  fernglenensis  than  any  of  the  other  species  here 
described,  but  it  is  a  proportionally  narrower  shell  with  more  convex 
valves 

Horizon.— Lower  Burlington  limestone. 

DlELASMA   BURLINGTONENKIS    (White) 

Plate  XXXI,  Figs.  45-49 

1860.  Terebratula  burlingtonensis  White,  Jour.  Boston  Soc.  Nat.  Hist.,  vol. 
7.  p.  228. 

Description. — Shell  below  medium  size,  elongate-ovate  in  outline,  the 
greatest  width  near  the  mid-length,  the  anterior  margin  rather  narrowly 
rounded.  The  dimensions  of  a  nearly  perfect  but  slightly  distorted  speci- 
men, a.  cotype,  are:  length  of  pedicle  valve  16.'  mm.,  length  of  brachial 
valve  15.1  mm.,  greatest  width  10.6  mm.,  thickness  7.5  mm.  A  large 
pedicle  valve  with  a  width  of  13.4  mm.  has  the  anterior  portion  too  in- 
complete to  allow  the  accurate  measurement  of  the  length  which  was 
probably  about  20  mm. 

Pedicle  valve  with  its  greatest  depth  posterior  to  the  middle,  arched 
from  beak  to  front  with  the  convexity  somewhat  greater  posteriorly,  the 
surface  curving  abruptly  from  the  median  line  to  the  postero-lateral  mar- 
gins, becoming  a  little  inflected  to  the  cardinal  extremities,  curving  more 
gently  to  the  antero-lateral  and  anterior  margins;  mesial  sinus  obsolete; 
beak  prominent,  only  slightly  incurved,  truncated  by  the  very  large,  sub- 
ovate  foramen  which  encroaches  wholly  upon  the  umbonal  region  of  the 
valve,  its  margin  fixing  a  plane  which  is  either  at  a  right  angle  to  the  plane 
of  the  valve  or  even  slopes  anteriorly  from  the  posterior  to  the  anterior 
margins  of  the  foramen ;  the  delthyrium  large,  its  greater  portion  filled 
by  the  beak  of  the  opposite  valve,  its  apex  closed  by  a  pair  of  deltidial 
plates.  Internally  the  foramen  is  bordered  by  a  distinct  pedicle  collar 
extending  towards  the  interior  of  the  valve ;  the  dental  lamella?  are  rather 
short  and  widely  separated. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  its  greatest  depth 
posterior  to  the  middle,  the  surface  curving  somewhat  abruptly  to  the 
postero-lateral  margins  and  more  gently  to  the  antero-lateral  and  anterior 
margins;  mesial  portion  of  the  valve  without  fold  or  sinus;  the  beak 
pointed  and  incurved  beneath  the  margin  of  the  deltidial  plates  of  the 
opposite  valve.  Internally  the  situation  of  the  crural  plates  separate  from 
the  socket  plates,  with  the  transverse,  muscle-bearing  plate  joining  the 
inner  surface  of  the  valve  medially,  may  be  recognized  from  the  position 
of  dark  lines  showing  upon  the  external  surface. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  very  indistinct, 
concentric  lines  of  growth. 


262  Mlssissil'i'l.W    BRACHIOPODA 

Hi  marks. — This  species  is  a  rare  one  and  has  not  been  available  in  suf- 
ficient numbers  to  make  it  possible  to  grind  any  examples  for  the  purpose 
of  determining  its  internal  characters.  The  interior  of  the  pedicle  valve, 
however,  is  perfectly  shown  in  one  of  the  cotypes,  and  the  essential  fea- 
tuies  of  the  genus  Dielasma  can  be  recognized  from  the  external  surface  of 
the  brachial  valve  of  another  cotype,  the  position  of  the  crural  lamellae 
and  the  transverse  muscle  plate  being  clearly  indicated  by  dark  lines. 
In  size,  and  in  the  entire  absence  of  fold  and  sinus,  the  species  resembles 
D.  formosa,  but  it  is  a  somewhat  more  slender  shell  with  less  convex  valves 
and  with  the  beak  of  the  pedicle  valve  less  incurved;  the  species  is  es- 
pecially characterized,  however,  by  the  large  size  of  the  foramen  which  is 
directed  straight  posteriorly  or  even  obliquely  away  from  the  brachial 
valve,  while  in  />.  formosa  the  foramen  is  directed  obliquely  postero- 
brachially.  The  concentric  growth  lines  of  the  shell  are  also  much  less 
conspicuous  in  this  species  than  in  I),  formosa. 

Horizon. —  Burlington  limestone. 

DlELASMA    SINUATA   U.    sp. 

Plate  XXXI,  Figs.  28-34 

1883.     Lhujula  craxvforelsvillensis  Gurley,  New    Carb.    Foss.,  Bull.  No.    1, 

p.  2. 
1895.     Melasma  formosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 

figs.  16-17  (not  figs.  12-15,  18-26). 
1906.     Dielasma  turgid/wm  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1309, 

pi.  19,  figs.  5-5a  (not  pi  22,  figs.  53-58). 
1906.     Dielasma  gorbyi  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1310, 

pi.  20,  fig.  5  (not  Terebratula  gorbyi  Miller). 

Description. — Shell  of  medium  size,  subovate  or  ovate-subpentagonal  in 
outline,  longer  than  wide,  the  greatest  width  near  the  mid-length  of  the 
shell,  the  anterior  margin  rounded,  nearly  straight  or  a  little  emarginate. 
The  dimensions  of  an  internal  cast,  somewhat  restored,  are :  length  of 
pedicle  valve  29.2  mm.,  length  of  brachial  valve  23.6  mm.,  greatest  width 
18.7  mm.,  thickness  20.9  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbonal  region  projecting  conspicuously  beyond  the  beak  of 
the  opposite  valve  in  full  grown  specimens,  the  surface  arched  from  beak 
to  front  with  the  curvature  becoming  progressively  more  convex  poste- 
riorly, the  lateral  slopes  curving  abruptly  and  steeply  from  the  median 
portion  of  the  valve  to  the  lateral  margins,  becoming  somewhat  inflected 
towards  the  cardinal  extremities,  the  lateral  margins  joining  those  of  the 
opposite  valve  in  a  broadly  obtuse  angle ;  mesial  sinus  originating  near 
the  middle  of  the  valve,  rather  narrow,  with  subparallel  sides,  rounded 
or  a  little  flattened  in  the  bottom,  its  lateral  borders  rounding  into  the 
lateral  slopes  of  the  valve,  of  moderate  depth  or  becoming  strongly  de- 


DIELASMA  263 

pressed  towards  the  front,  sometimes  produced  anteriorly  in  a  short, 
rounded,  lingual  extension ;  beak  prominent,  strongly  incurved,  pierced 
by  a.  large  foramen  which  encroaches  wholly  upon  the  umbonal  region, 
being  in  contact  with  the  delthyrium  only  at  its  apex ;  delthyrium  broadly 
triangular,  hidden  by  the  incurvature  of  the  beak.  Internally  the  dental 
lamelhe  are  well  developed  and  of  moderate  length,  the  muscular  scars 
obscure  or  obsolete. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  pos- 
terior to  the  middle,  the  surface  arched  from  beak  to  front  with  the 
curvature  becoming  continuously  more  convex  towards  the  beak,  the 
lateral  slopes  convex,  curving  abruptly  from  the  median  line  to  the  lateral 
margins ;  mesial  portion  of  the  valve  not  differentiated  as  a  fold  to  cor- 
respond with  the  sinus  of  the  opposite  valve,  but  the  anterior  margin 
commonly  exhibits  a  rounded  sinuosity  to  correspond  with  the  short  lin- 
gual extension  of  the  opposite  valve ;  beak  pointed  and  incurved  beneath 
that  of  the  opposite  valve.  Internally  the  crural  plates  are  separated  from 
the  socket  plates  and  diverge  anteriorly,  at  the  beak  they  are  low, 
angular  ridges  but  become  thin,  rather  highly  elevated  lamellae  an- 
teriorly, they  are  joined  transversely  by  a  concave  plate  bearing  the 
muscular  scars  which  is  attached  to  the  inner  surface  of  the  valve  along  its 
median  line,  leaving  a  pair  of  triangular,  finger-like  cavities  converging 
towards  the  beak,  which  are  surrounded  by  the  inner  surfaces  of  the  base 
of  the  crural  plates,  the  muscle  plate  and  the  inner  surface  of  the  valve ; 
anteriorly  the  muscle-bearing  plate  extends  considerably  beyond  the  ter- 
mination of  the  attached  portion  of  the  crural  lamella? ;  the  muscle  scars 
are  commonly  rather  strongly  impressed  upon  the  surface  of  the  concave 
muscle  plate. 

Surface  of  both  valves  smooth  externally  except  for  the  presence  of  con- 
centric lines  of  growth  which  vary  greatly  in  strength  upon  different 
individuals ;  upon  some  internal  casts  exceedingly  faint  radiating  costag 
are  sometimes  distinguishable  towards  the  lateral  and  anterior  margins. 

Remarks. — This  species  has  been  identified  sometimes  as  Girtyella  turgida, 
but  besides  being  a  much  larger  species  and  lacking  the  mesial  depression 
of  the  brachial  valve  towards  the  front,  the  internal  structure  of  the 
rostral  portion  of  the  brachial  valve  is  totally  different  and  the  two  species 
cannot  even  be  included  in  the  same  genus.  The  brachial  valve  of  the 
species  has  been  identified  sometimes  as  D.  formosa,  but  it  differs  from 
the  corresponding  valve  of  that  species  in  being  somewhat  flatter  medi- 
ally, in  having  a  less  pointed  anterior  outline,  and  in  having  the  mesial 
sinuosity  in  the  anterior  margin  for  the  accommodation  of  the  anterior 
extremity  of  the  sinus  of  the  opposite  valve. 

Horizon. — Keokuk  limestone,  Salem  limestone. 


2ti4  MISSISSDPPIAN   BRACHIOPODA 

DlELASMA    INFLATA    11.    Sp. 

Plate  XXXII,  Figs.  18-28 

1S!>4.     Dielasma  turgida  Ball  and  Clarke,  Int.  to  Study  of  Brach.,  pi.  53. 

fig.  12  (not   figs.  10-11  ). 
IS!).").      Ditlasma  turgida  Had  and  Clarke.  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 

fig.  4  (not  figs.  l-:5,  5-8). 

Description. — Shell  below  medium  size,  longer  than  wide,  subovate  or 
subangularly  subpentagonal  in  outline,  the  greatest  width  near  or  ante- 
rior to  the  middle,  the  anterior  margin  emarginate  or  slightly  convex,  the 
valves  gibbous,  often  geniculate  near  the    middle,    the    thickness  of  the 

shell   sonieti s  exceeding  the  width.     The  dimensions  of  two  complete 

examples  are:  length  of  pedicle  valve  13.5  mm.  and  16.8  mm.,  length  of 
brachial  valve  11.5  mm.,  and  14.6  mm.,  greatest  width  8.2  mm.  and  12  mm., 
thickness  9.8  mm.  and  12.2  mm. 

Pedicle  valve  gibbous,  the  curvature  abruptly  changed  in  mature  ex- 
amples near  the  mid-length  of  the  valve,  where  it  is  bent  in  a  subgenicu- 
late  manner,  the  curvature  to  the  postero-lateral  margins  is  abrupt,  the 
surface  becoming  inflected  to  the  cardinal  extremities,  towards  the 
antcro-lateral  and  anterior  margins  the  curvature  is  rather  gently  convex 
to  the  line  of  geniculation,  beyond  which  the  surface  drops  abruptly  to  the 
margins;  mesial  sinus  originating  at  the  line  of  geniculation,  usually  flat 
in  the  bottom,  slightly  or  strongly  depressed  towards  the  margin,  the 
median,  flattened  portion  a  little  produced  anteriorly  in  a  short,  rounded, 
lingual  extension ;  beak  prominent,  strongly  incurved,  its  apex  nearly  or 
quite  in  contact  with  the  umbo  of  the  opposite  valve,  pierced  by  a  large, 
subovate  foramen  which  encroaches  wholly  upon  the  umbonal  region  of 
the  valve,  the  delthyrium  hidden  by  the  incurvature  of  the  beak,  in  con- 
tact with  the  foramen  only  at  its  apex,  entirely  filled  by  the  pseudodel- 
tidium.  Internally  the  dental  lamellae  are  well  developed  and  reach  an- 
teriorly from  the  beak  nearly  one-fourth  the  total  length  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  surface  genicu- 
late as  in  the  opposite  valve,  curving  rather  abruptly  to  the  postero- 
lateral margins  and  more  gently  to  the  antero-lateral  and  anterior  mar- 
gins up  to  the  line  of  geniculation  beyond  which  it  drops  abruptly  to  the 
margin ;  in  front  of  the  line  of  geniculation  the  median  portion  of  the 
valve  is  marked  by  three  longitudinal  folds  separated  by  subangular  or 
rounded  furrows,  the  median  one  of  the  three  folds  is  opposite  the  slight 
lingual  extension  from  the  anterior  margin  of  the  sinus  of  the  pedicle 
valve,  it  may  be  somewhat  elevated  above  the  two  lateral  folds,  even  with 
them  or  depressed  between  them ;  the  beak  pointed,  incurved  beneath 
that  of  the  opposite  valve.  Internally  the  socket  plates  are  distinct  from 
the  crural  plates,  the  latter  are  attached  to  the  inner  surface  of  the  valve 
for  more  than  one-fourth  its  length  anteriorly  from  the  beak,  a  little  less 


DIELASMA  265 

than  half  way  between  the  median  line  of  the  valve  and  the  lateral  mar- 
gins, the  crural  plates  are  joined  transversely  by  a  concave  plate  bearing 
the  muscle  scars,  which  is  in  contact  with  the  inner  surface  of  the  valve 
medially,  leaving  a  pair  of  finger-like,  triangular  cavities  converging  and 
diminishing  in  size  towards  the  beak,  each  bounded  by  the  base  of  a  crural 
plate,  the  muscle  plate  and  the  inner  surface  of  the  valve. 

Surface  of  both  valves  smooth  posterior  to  the  line  of  geniculation,  but 
anterior  to  this  line  it  is  marked  by  more  or  less  conspicuous  concentric 
lines  of  growth.     The  shell  structure  finely  punctate. 

R(  marks.  —  This  species  is  one  of  those  which  has  commonly  been  referred 
to  Girtyella  turgida,  but  besides  possessing  characters  of  the  rostral  portion 
of  the  brachial  valve  which  are  generically  different  from  that  species,  the 
external  configuration  of  the  shell  is  very  different.  The  shell  attains  a 
much  larger  size  than  G.  turgida,  and  differs  from  it  in  the  geniculate  habit 
of  growth  of  the  shell,  and  also  in  the  much  more  conspicuous  triplication 
of  the  brachial  valve  towards  the  anterior  margin.  The  more  conspicu- 
ous variations  observed  in  the  species  are  the  proportional  width  of  the 
shell  and  the  depth  of  the  mesial  sinus.  In  some  examples  the  width  and 
thickness  of  the  shell  is  nearly  equal,  while  in  others  the  thickness  ex- 
ceeds the  width  to  a  notable  degree.  The  internal  characters  of  the 
rostral  portion  of  the  brachial  valve  have  been  determined  only  from  the 
markings  of  the  septa  as  seen  upon  the  exfoliated  external  surface,  but 
these  clearly  indicate  the  genus  Dielasma. 

Horizon. — Salem  limestone. 

Dielasma  formosum  (Hall) 

Plate  XXXIII,  Figs.  12-17 

1856.     Terebratula  formosa  Hall,  Trans.  Albanv  Inst.,  vol.  4,  p.  6. 
1882.     Ten  bratula  formosa  White,  11th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  361, 
pi.  39,  figs.  6-8. 

1882.  Terebratula  formosa  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

p.  55,  pi.  6.  has.  59-64. 

1883.  Terebratula  formosa  Hall,  12th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  337, 

pi.  2!),  ligs.  59-64. 

1894.  Dielasma  formosa  Hall  and  Clarke.  Int.  to  Study  of  Brack.,  pt.  2, 

pi.  53,  figs.  15-17  (not  18-19). 

1895.  Dielasma  formosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  81, 

figs.  18-23,  25-26  (not  figs.  12-17,  24). 
1895.     Dielasma  obovata  Hall  and  Clarke,  Pal.  X.  Y.,  vol.  8,  pt.  2,  pi.  81, 

figs.  38-40. 
1897.     Dielasma  obovata  Hall  and  Clarke,  14th  Ann.  Rep.  N.  Y.  State  Geol., 

p.  372,  pi.  14.  figs.  12-14. 
1906.     Dielasma  formosum  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind..  p.  1310, 

pi.  22.  figs.  59-64. 
1911.     Dielasma  formosa  Weller,  Jour.  Geol.,  vol.  19,  p.  440,  figs.  la-n. 


266  MISSISSIPPIAN    BRACHIOPODA 

Description. — Shell  usually  below  medium  size,  elongate-ovate  in  outline, 
the  greatesl  width  oear  or  anterior  to  the  middle,  the  anterior  margin 
rounded.  The  dimensions  of  a  very  p'erfecl  specimen  are:  length  of  ped- 
icle valve  15.4  mm.,  length  of  brachial  valve  13.8  nun.,  maximum  width 
10.2  nun.,  thickness  9  nun. 

Pedicle  valve  most  convex  posterior  to  the  middle,  arched  along  the 
median  line  from  beat  to  Front  with  a  convexity  progressively  increasing 
posteriorly,  the  surface  curving  abruptly  from  the  median  line  to  the 
postero-lateral  margins  and  becoming  inflected  to  the  cardinal  extremi- 
ties, curving  more  gently  to  the  antero-lateral  margins;  mesial  sinus  obso- 
lete; beak  prominent,  incurved,  pierced  by  a  Large,  subcircular  or  subo- 
vate  foramen  which  encroaches  wholly  upon  the  umbonal  region  of  the 
valve,  in  contact  with  the  delthyrium  only  at  its  apex;  delthyrium  broadly 
triangular,  entirely  closed,  except  around  the  border,  by  the  beak  of  the 
opposite  valve  and  the  deltidial  plates  which  are  invisible  externally,  be- 
cause of  the  incurvature  of  the  beak.  Internally  the  dental  lamella*  are 
well  developed  aud  extend  anteriorly  from  the  beak  for  nearly  one-fourth 
the  total  length  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  or  a  little  posterior  to  the  middle,  arched  from  beak  to  front 
along  the  median  line  -with  the  curvature  a  little  greater  posteriorly,  the 
surface  curving  rather  abruptly  from  the  median  line  to  the  postero- 
lateral margins,  becoming  more  gently  curved  anteriorly;  mesial  portion 
of  the  valve  not  differentiated  as  fold  or  sinus ;  the  beak  acutely  pointed, 
incurved  beneath  that  of  the  opposite  valve.  Internally  the  socket  plates 
are  separate  from  the  crural  plates  and  are  not  connected  by  a  hinge- 
plate;  the  crural  plates  oi-iginate  near  the  apex  of  the  valve  about  half 
way  between  the  median  line  and  the  lateral  margins,  gradually  approach- 
ing, relatively,  the  median  line  anteriorly,  they  are  low  and  strongly  in- 
clined inward  posteriorly,  abruptly  becoming  very  greatly  increased  in 
height  anteriorly  and  becoming  more  erect,  posteriorly  they  are  joined  by 
a  concave,  platform-like  plate  bearing  the  muscular  scars,  which  is  medi- 
ally in  contact  with  the  inner  surface  of  the  valve  leaving  a  pair  of  tri- 
angular, finger-like  cavities  diverging  from  the  beak,  which  are  surround- 
ed by  the  inner  surfaces  of  the  crural  plates,  the  muscle  plate  and  the 
floor  of  the  valve ;  the  brachidium  is  short,  its  anterior  extremity  falling 
short  of  the  middle  of  the  valve. 

Surface  of  both  valves  nearly  smooth  or  marked  only  by  concentric 
lines  of  growth  which  are  sometimes  strongly  developed  and  rather  closely 
crowded.     Shell  structure  finely  punctate. 

Remarks. — Various  forms  have  been  referred  to  this  species  in  the  liter- 
ature. In  volume  eight  of  the  New  York  Paleontology  no  less  than  four 
distinct  species  belonging  to  two  different  genera  are  illustrated  under 


DIELASMA  267 

the  name  I),  formosa,  and  most  of  the  loop  bearing  shells  of  the  Mississip- 
pian  faunas  commonly  have  been  referred,  in  recent  years,  either  to  this 
species  or  to  (lirtyclla  turgida.  The  species  is  a  well-defined  one,  character- 
ized by  the  ovate  outline  of  the  shell,  rounded  in  front,  with  neither  fold 
or  sinus  in  either  valve.  The  shell  described  by  Hall  and  Clarke  as  D. 
obovata  and  said  to  be  from  the  Pennsylvanian  is  evidently  a  large  example 
of  this  species.  The  original  label  with  the  type  specimen  is  marked 
"Carboniferous  Limestone,  Kentucky,"  with  no  suggestion  that  it  came 
from  the  Pennsylvanian.  Furthermore,  the  lithologic  character  of  the 
specimen  is  identical  with  specimens  from  the  Salem  limestone  of  southern 
Indiana  or  Kentucky,  the  typical  horizon  for  Didasma  formosa. 
Horizon.  —  Salem  limestone. 

DlELASMA   ILLINOISENSIS    11.    sp. 

Plate  XXXIII,  Figs.  18-20 

Description. — Shell  below  medium  size,  elongate  subovate  in  outline,  the 
greatest  width  near  the  mid-length,  the  anterior  margin  rounded.  The 
dimensions  of  a  nearly  perfect  specimen  are :  length  of  pedicle  valve 
21  mm.,  length  of  brachial  valve  18.8  mm.,  greatest  width  12.7  mm.,  thick- 
ness 10  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  arcuate  from  beak  to  front  along  the  median 
line  with  the  curvature  increasingly  convex  posteriorly,  the  convexity  at 
first  moderate  from  the  median  line  towards  the  postero-lateral  margins, 
curving  more  abruptly  as  it  approaches  the  margin  and  becoming  inflected 
to  the  cardinal  extremities,  the  curvature  more  gentle  towards  the  antero- 
lateral margins ;  mesial  sinus  of  moderate  width  and  depth,  rounded  in 
the  bottom,  originating  near  or  a.  little  posterior  to  the  middle  of  the 
valve;  the  beak  prominent  and  closely  incurved,  the  foramen  large,  sub- 
circular  or  subovate  in  outline,  encroaching  wholly  upon  the  umbonal 
portion  of  the  valve,  the  deltidial  plates  hidden  by  the  incurvature  of 
the  beak.  Internally  the  dental  lamella'  are  well  developed  and  of  mod- 
erate length. 


Q 


o  \>  w  w  o 


Fie.  30. — A  series  of  seven  cross-sections  of  the  rostral  portion  of  the  shell  of 
Bielasma  illinoisensis  (X  2%),  showing  the  dental  lamella^  of  the  pedicle  valve, 
and  the  crural  lamella?  developed  independently  from  the  socket  plates. 

The  brachial  valve  less  convex  than  the  pedicle,  gently  convex  longi- 
tudinally from  beak  to  front,  the  curvature  tisually  a  little  greater  near 


268  MISSISSIPPI^    BRACHIOPOD.A 

the  beak,  sometimes  nearly  straight  towards  the  anterior  margin,  trans- 
versely it  is  strongly  convex  with  the  curvature  more  abrupt  towards  the 
posterolateral  margins;  mesial  portion  of  the  valve  not  differentiated 
from  the  general  curvature  of  the  surface,  or  elevated  in  a  slight  mesial 
fold  near  the  anterior  margin  ;  beak  sharply  pointed,  incurved  beneath  the 
pseudodeltidium  of  the  opposite  valve.  Internally  the  crural  plates  are 
distinct  from  the  socket  plates  and  diverge  anteriorly  from  the  beak, 
being  attached  to  the  inner  surface  of  the  valve  for  nearly  one-fourth 
the  length  of  the  valve;  the  concave  muscle  bearing  plate  joins  the  inner 
surface  of  the  valve  along  its  median  line  and  extends  anteriorly  about 
two-lift hs  the  length  of  the  valve. 

Surface  of  both  valves  nearly  smooth,  marked  oidy  by  rather  incon- 
spicuous  lines  of  growth.     The  shell   structure  finely  punctate. 

Remarks. — This  species  differs  from  P.  sinuata  in  its  smaller  size,  less 
strongly  convex  valves,  especially  the  less  longitudinal  convexity  of  the 
brachial  valve,  and  ill  its  more  slender  form. 

Horizon. — Chester  group,  Taint  Creek  formation. 

DlELASMA   SHUMABDANUM    (Miller) 

Plate  XXXI,  Figs.  25-27 

L863.     Terebratula  arcuata  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2, 

p.  83.     (Not  T.  arcuata  Roemer,  1840.) 
1883.     Terebratula  sliumardana  Miller,  Am.  Pal.  Foss.,  2nd  ed.,  p.  299. 

Description. — Shell  of  medium  size  or  a  little  larger,  elongate  subovate 
in  outline,  with  the  greatest  width  well  towards  the  anterior,  the  anterior 
margin  rounded,  the  posterolateral  margins  gently  convex.  The  dimen- 
sions of  a  nearly  perfect  specimen  are :  length  of  pedicle  valve  29  mm., 
length  of  brachial  valve  26.5  mm.,  greatest  width  19.6  mm.,  thickness 
14.5  mm. 

Pedicle  valve  strongly  arcuate  from  beak  to  front,  the  curvature  in- 
creasingly convex  towards  the  beak,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  broadly  flattened,  gently  convex  transversely  in 
the  posterior  portion  of  the  valve  to  near  the  postero-lateral  margins 
where  it  is  rather  abruptly  curved  towards  the  opposite  valve  and  in- 
flected towards  the  cardinal  extremities,  anteriorly  the  surface  is  gently 
convex  to  the  lateral  margins ;  mesial  sinus  narrow  and  shallow,  originat- 
ing at  or  near  the  beak,  not  sharply  defined  along  its  lateral  margins ; 
the  beak  truncated,  incurved,  the  foramen  large,  subovate,  encroaching 
wholly  upon  the  umbonal  portion  of  the  valve,  the  deltidial  plates  hidden 
by  the  incurvature  of  the  beak.  Internally  the  dental  lamella?  are  well 
developed  and  of  moderate  length. 

Brachial  valve  gently  convex  from  beak  to  front  along  the  median 
line  with  the  highest  point  near  the  middle,  strongly  convex  transversely 


MELASMA  269 

with  the  curvature  more  abrupt  to  the  postero-lateral  margins;  the  mesial 
portion  of  the  valve  either  not  differentiated  from  the  general  convexity, 
or  elevated  in  a  slight,  obscure,  mesial  fold  near  the  front;  beak  sharply 
pointed,  incurved  beneath  the  deltidial  plates  of  the  opposite  valve. 
Internally  the  socket  plates  and  crural  plates  are  distinct,  the  lines  of  at- 
tachment of  the  crural  plates  to  the  inner  surface  of  the  valve  diverge 
from  the  beak  and  extend  anteriorly  about  one-fourth  the  length  of  the 
valve;  the  concave  muscle  bearing  plate  between  the  crural  lamellae  is 
emarginate  in  front  and  extends  anteriorly  from  the  beak  about  two- 
fifths  the  total  length  of  the  valve,  it  is  marked  by  fine  concentric 
wrinkles  parallel  with  the  anterior  margin  of  the  plate  and  discontinuous 
along  a  narrow  median  line. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  more  or  less 
obscure  concentric  lines  of  growth.     Shell  structure  finely  punctate. 

Remarks. — This  species  has  not  been  commonly  recognized  since  its 
original  definition  by  Swallow  as  Terebratula  arcuata,  and  it  seems  to  be 
a  rather  rare  species.  In  its  arcuate  form  the  shell  resembles  the  Pennsyl- 
vanian  species  D.  bovidens,  and  it  has  sometimes  been  so  identified,  but  it  is 
somewhat  more  elongate  than  that  species,  less  strongly  arcuate,  and  the 
median  sinus  of  the  pedicle  valve  is  much  narrower. 

Horizon.  —  Chester  Group,  Okaw  formation. 

DlELASMA    ARKANSANUM    n.    Sp. 

Plate  XXXI,  Figs.  35-44 

Description. — Shell  about  medium  size,  subovate  in  outline,  longer  than 
wide,  the  greatest  width  a  little  in  front  of  the  middle.  The  dimensions 
of  a  nearly  complete  specimen  are :  length  of  pedicle  valve  30.5  mm., 
length  of  brachial  valve  28.2  mm.,  greatest  width  21  mm.,  thickness 
14  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  arched  longitudinally  from  beak  to  front  with 
the  curvature  becoming  progressively  more  convex  posteriorly,  from  the 
umbonal  region  the  surface  is  moderately  convex  to  near  the  postero- 
lateral margins,  where  it  is  more  abruptly  curved  and  inflected  towards 
the  cardinal  extremities,  towards  the  antero-lateral  and  anterior  margins 
the  convexity  is  more  gentle ;  mesial  sinus  narrow  and  very  shallow, 
ill-defined  laterally,  originating  at  or  near  the  mid-length  of  the  valve, 
frequently  nearly  or  quite  obsolete ;  beak  strongly  incurved,  pierced  by  a 
large,  oblique,  subovate  foramen  which  encroaches  wholly  upon  the 
umbonal  portion  of  the  valve,  the  deltidial  plates  hidden  by  the  in- 
curvature of  the  beak.  Internally  the  dental  plates  are  well  developed 
and  of  moderate  length. 


270  MISSISSIPPIAN    BRACHIOPODA 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity  near 
or  posterior  to  the  middle,  the  surface  curving  rather  abruptly  from  the 
median  line  to  the  post ero-lateral  margins  and  more  gently  to  the  antero- 
lateral and  anterior  margins ;  mesial  portion  of  the  valve  not  differentiated 
from  the  general  convexity  of  the  valve;  the  beak  acutely  pointed  and 
incurved  beneath  the  pseudodeltidium  of  the  opposite  valve,  internally 
the  socket  plates  and  crural  plates  are  distinct,  the  attachment  of  the 
crural  plates  to  the  inner  surface  of  the  valve  diverging  from  the  apex 
and  extending  anteriorly  for  about  one-fourth  the  length  of  the  valve; 
the  concave  muscle  bearing  plate  lying  between  the  crural  plates  is 
elongate,  rounded  in  front,  and  extends  anteriorly  about  two-fifths  the 
length  of  the  valve;  it  is  marked  by  strong  concentric  wrinkles  parallel 
with  the  anterior  margin  winch  are  discontinuous  along  a  narrow  median 
line. 

Surface  of  both  valves  smooth  or  nearly  smooth,  marked  only  by 
generally  obscure,  concentric  lines  of  growth.  Shell  structure  finely  and 
closely  punctate. 

Remarks.- — In  general  form  this  species  resembles  D.  fvrmosa,  but  it  is 
proportionally  a  broader  and  thinner  shell  with  the  greatest  width  situated 
more  anteriorly,  it  also  usually  differs  from  that  species  in  having  a  slight 
median  sinus  in  the  pedicle  valve  which  is  absent  in  D.  formosa.  The  form 
of  the  shell  perhaps  more  closely  resembles  D.  cliouteauensis,  but  that  species 
lacks  the  median  sinus  of  the  pedicle  valve  and  does  not  have  its  greatest 
width  anterior  to  the  middle. 

Locality. — Washington  County,  Arkansas;  Webb  City,  Missouri  (Carter- 
ville  formation?). 

DlELASMA   SUBSPATULATUM   n.   Sp. 

Plate  XXXIII,  Figs.  6-11 

Description. — Shell  below  medium  size,  elongate-subovate  in  outline, 
the  width  much  greater  than  the  thickness,  the  greatest  width  towards 
the  front  of  the  shell,  the  postero-lateral  margins  elongate  and  gently 
convex.  The  dimensions  of  a  nearly  complete  specimen  are :  length  of 
pedicle  valve  19  mm.,  length  of  brachial  valve  17.5  mm.,  greatest  width 
14.1  mm.,  thickness  8.2  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  near  or  pos- 
terior to  the  middle,  arched  from  beak  to  front  along  the  median  line 
with  the  curvature  a  little  more  convex  posteriorly,  the  surface  gently 
convex  transversely,  but  as  it  approaches  the  postero-lateral  margins  it 
is  abruptly  curved  towards  the  opposite  valve  and  becomes  inflected 
towards  the  cardinal  extremities ;  the  mesial  sinus  obsolete ;  the  beak 
incurved,  perforated  by  a  large  foramen  which  encroaches  upon  the 
umbonal  portion  of  the  valve.  Internally  the  dental  plates  are  well  de- 
veloped and  are  of  moderate  length. 


..     GIRTYELLA  271 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  along  the  median  line  from  the  beak  to  the 
front  the  surface  is  gently  convex  with  the  curvature  a  little  greater 
posteriorly,  from  the  middle  of  the  valve  to  the  front  the  surface  is 
sometimes  almost  straight,  transversely  it  is  gently  depressed  convex 
towards  the  front  but  becomes  more  convex  posteriorly  because  of  the 
decreasing  width  of  the  valve ;  mesial  portion  of  the  valve  somewhat 
broadly  flattened  with  no  fold  or  sinus;  the  beak  pointed,  incurved 
beneath  that  of  the  opposite  valve.  Internally  the  crural  plates  are 
entirely  separate  from  the  socket  plates,  they  diverge  from  the  apex  of 
the  valve  and  rise  from  its  inner  surface,  the  attachment  extending 
from  the  beak  for  nearly  one-fourth  the  length  of  the  valve ;  between 
the  crural  plates  the  concave  muscle-bearing  plate  extends  anteriorly  in 
the  median  line  of  the  valve  some  distance  beyond  the  attachment  of  the 
crural  plates  and  terminates  in  a  point. 

Surface  of  both  valves  nearly  smooth  or  marked  by  obscure  concentric 
lines  of  growth.     ShelJ  structure  finely  punctate. 

I!<  marks. — This  species  is  especially  characterized  by  the  broad,  trans- 
versely flattened  pedicle  valve,  the  absence  of  mesial  fold  or  sinus  in 
both  valves,  the  gentle  longitudinal  convexity  of  the  brachial  valve,  and 
the  anterior  position  of  the  greatest  width  of  the  shell.  It  is  somewhat 
similar  to  D.  bovidms  of  the  Pennsylvania!!  faunas  but  entirely  lacks  the 
sinus  of  the  pedicle  valve  which  is  characteristic  of  that  species. 

Locality. — Washington  County,  Arkansas. 

Genus  GIRTYELLA  Weller 
Description. — Shell  terebratuliform,  the  pedicle  valve  sinuate,  with  a 
large,  subcircular  or  subovate,  oblique  foramen  which  encroaches  upon 
the  umbo;  the  brachial  valve  frequently  sinuate  and  often  with  a  slight 
median  fold  in  the  bottom  of  the  sinus.  Internally  the  dental  lamellae 
are  well  developed  in  the  pedicle  valve.  In  the  brachial  valve  the  socket 
plates  are  joined  by  a  concave  hinge-plate  which  is  imperforate  at  the 
apex  and  is  supported  by  a  median  septum ;  the  inner  sides  of  the  dental 


Fig.  31. — A  series  of  nine  cross-sections  of  the  rostral  portion  of  the  shell  ot 
Girtyella  indianensis  (X  2V2)  from  the  Pella  beds,  showing  the  dental  lamellae 
of  the  pedicle  valve,  and  the  median  septum,  hinge-plate,  and  manner  of 
formation  of  the  crura  in  the  brachial  valve. 


-72  MISSISSIPPI  \.\    BRACHIOPODA 

sockets  retreat  from  the  margins  of  the  valve  anteriorly  beyond  the 
point  of  articulation  and  become  the  liases  of  the  crura  which  are  still 
joined  by  the  concave  binge-plate  and  are  also  supported  by  Lamella: 
resting  againsl  the  inner  surface  of  the  lateral  slopes  of  the  valve.  The 
brachidium  short,  its  free  portion  apparently  being  like  that  of  Dielasma 

and   not    reaching  to  the   middle  of  the  shell. 

Remarks. — Members  of  this  genus  have  commonly  been  included  in  the 
genua  Dielasma,  but  they  differ  fundamentally  from  that  go-mas  in  the 
presence  of  a  median  septum  supporting  the  hinge-plate  of  the  brachial 
valve,  and  in  the  origin  of  the  bases  of  the  crura  from  the  socket  plates. 
In  his  description  of  the  species  which  is  selected  as  the  genotype,  Girty 
referred  the  form  to  the  genus  Harttina  on  account  of  the  presence  of  a 
median  seplum  in  the  pedicle  valve,  but  the  brachidium  of  Harttina  is 
elongate,  like  that  of  Cryptonella,  reaching  nearly  to  the  front  of  the  shell, 
while  thai  of  Girtyella  is  short  like  the  brachidium  of  Dielasma, 

(ilKTVKI.I.A  CEDARENSIS  n.  sp. 

Plate  XXXIV,  Figs.  48-50 

Description. — Shell  below  medium  size,  subovate  in  outline,  the  greatest 
width  anterior  to  the  middle,  the  anterior  margin  subtruncate.  The 
dimensions  of  a  nearly  complete  internal  cast  are:  length  of  pedicle 
valve  18.5  mm.,  length  of  brachial  valve  16  mm.,  greatest  width  IT). 2 
mm.,  thickness  11.9  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  postero-lateral  margins  and  becoming  somewhat  inflected 
to  the  cardinal  extremities,  curving  less  abruptly  to  the  antero-lateral  and 
anterior  margins ;  mesial  sinus  shallow,  rounded  in  the  bottom,  rather 
broad  and  ill-defined  laterally,  originating  near  the  middle  of  the  valve; 
beak  rather  prominent  and  incurved,  character  of  the  foramen  not  shown 
in  the  type  specimen.  Internally  the  dental  plates  are  rather  strong  and 
extend  anteriorly  from  the  beak  between  one-fifth  and  one-fourth  the 
length  of  the  valve,  with  only  a  small  amount  of  divergence. 

Brachial  valve  about  equally  convex  with  the  pedicle,  the  greatest 
convexity  near  the  middle,  the  surface  curving  a  little  more  abruptly  to 
the  anterior  and  antero-lateral  margins  than  posteriorly ;  mesial  fold 
obsolete,  but  with  the  mesial  portion  of  the  valve  obscurely  flattened 
anterior  to  the  middle  of  the  valve ,  the  beak  pointed  and  incurvod  beneath 
that  of  the. opposite  valve.  Internally  a  strong  median  septum  extends 
anteriorly  from  the  beak  for  about  two-fifths  the  length  of  the  valve ;  the 
characters  of  the  hinge-plate  not  fully  observed,  but  so  far  as  determined 
agreeing  entirely  with  other  species  of  Girtyella. 

Surface  of  both  valves  marked  by  concentric  lines  of  growth  which 
become  stronger  and  more  crowded  towards  the  margin. 


GIRTYELLA  273 

Hi  marks. — The  holotype  of  this  species  is  a  nearly  complete  internal 
cast  in  which  the  dental  Lamellae  of  the  pedicle  valve  and  the  median 
septum  of  the  brachial  valve  are  clearly  exhibited  as  slits.  The  species 
is  referred  to  the  genus  Girtyella  because  of  the  strong  median  septum  of 
the  brachial  valve,  and,  although  the  characters  of  the  hinge-plate  are  not 
clearly  shown  in  the  specimen,  there  can  be  no  doubt  as  to  the  correct 
generic  reference  of  the  species.  The  species  is  the  largest  member  of  the 
genus  here  recognized,  and  seems  to  agree  more  closely  with  G.  iitdianensis 
than  with  any  other,  but  the  shell  is  proportionally  broader  and  more 
rotund  in  contour  than  that  species. 

Horizon. — North  view  shale  and  upper  Chouteau  limestone  of  the  Kin- 
derhook. 

Girtyella  turgida  (Hall) 
Plate  XXXIV,  Figs.  25-36 

1856.     Terebratula  turgida  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  6. 

1882.  Terebratula  turgida  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol    1, 

p.  54.,  pl  6,  figs.  53-58. 

1883.  Terebratula  turgida  Hall,  12th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  336, 

pl.  29,  figs.  53-58. 

1893.  Dielasma   turgida  Tieecher  and  Schuehert,  Proc.  Biol.   Soc.  Wash., 

vol.  8.  pp.  71-74,  pl.  10,  figs.  1-6. 

1894.  Dielasma  turgida  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pl.  53,  fie-.  11  (not  figs.  10.  12). 

1895.  Dielasma  turgida  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pl.  81, 

figs.  5-6  (not  figs.  1-4,  7-8). 
1906.     Dielasma  turgidum  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p   1309, 

pl.  22.  figs,"  53-58   (not  pl.  19,  figs.  5-5a). 
1911.     Girtyella  turgida  Weller,  Jour.  Geol.,  vol.  19,  p.  443. 

Description.  —  Shell  small,  subovate  or  subpentagonal  in  outline,  the 
anterior  margin  usually  emarginate  but  sometimes  straight,  the  greatest 
width  near  or  anterior  to  the  middle,  sometimes  nearly  at  the  front  of 
the  shell,  the  valves  more  or  less  gibbous.  The  dimensions  of  two  indi- 
viduals, the  larger  one  an  exceedingly  gibbous  example,  are:  length  of 
pedicle  valve  7.7  mm.  and  8.3  mm.,  length  of  brachial  valve  6.6  mm. 
and  6.8  mm.,  greatest  width  6.2  mm.  and  6.1  mm.,  thickness  5.2  mm. 
and  7.2  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  from  the  umbonal  region  to  the  postero-lateral  margins,  be- 
coming inflected  towards  the  cardinal  extremities,  curving  more  gently 
to  the  antero-lateral  and  anterior  margins ;  mesial  sinus  originating  in 
or  just  in  front  of  the  umbonal  region,  of  modei*ate  width,  its  lateral 
boundaries  rounding  into  the  lateral  slopes,  rounded  in  the  bottom  and 
often  becoming  rather  deep  anteriorly;  the  beak  prominent,  rather  blunt, 


L'74  MISSISSIPPIAN    BRACHIOPODA 

Btrongly  incurved,  coming  nearly  or  qnite  in  contad  with  the  ombona] 
region  of  the  opposite  valve,  pierced  by  a  Large,  oblique,  subovate  or 
subelliptical  foramen  which  encroaches  upon  the  umbonal  region,  coming 
in  contad  with  the  delthyrium  only  a1  its  apex.  Internally  the  dental 
lamella'  are  well  developed  and  extend  anteriorly  from  the  beak  with  bijt 
slight  divergence  for  about  one  -fourth  the  length  of  the  valve. 

Brachial  valve  nearly  equally  convex  with  the  pedicle,  the  greatest 
convexity  posterior  to  the  middle,  the  umbo  prominent,  the  surface 
curving  abruptly  to  the  posterior  and  postero-lateral  margins,  the  curva- 
ture  becoming   more   gentle   to   the  a nl ero-lat eral   and    anterior  margins; 

t     *      *      «      \f      \t/      y^y 

F  G 

Fig.   32. — A  series  of  seven   cross-sections  of   the   rostral   portion   of  the   brachial 
valve  of  Oirtyella  turgida  (X  2V2),  showing  the  median  septum  supporting  the. 
hinge-plate,  and  the  manner  of  formation  of  the  crura. 

mesial  portion  of  the  valve  depressed  in  a  sinus  originating  in  front  of 
the  umbonal  region,  which  is  somewhat  broader,  shallower  and  flatter 
than  that  of  the  pedicle  valve,  occasionally  a  slight,  rounded  rib  occupies 
the  median  line  of  the  sinus  towards  the  front;  the  beak  pointed  and 
incurved  beneath  that  of  the  opposite  valve.  Internally  the  socket  plates 
are  joined  by  a  concave  hinge-plate  which  is  supported  by  a  median 
septum,  anteriorly  the  socket  plates  retreat  from  the  lateral  margins  of 
the  valve  but  are  still  joined  together  by  the  binge-plate  and  are  joined 
to  the  inner  surface  of  the  lateral  slopes  of  the  valve  until  they  are 
continued  into  the  free  bases  of  the  crura ;  the  brachidium  short,  not 
reaching  to  the  middle  of  the  valve. 

Surface  of  both  valves  sometimes  nearly  smooth  but  usually  marked 
by  concentric  lines  of  growth  which  vary  greatly  in  strength  and  dis- 
tribution in  different  examples ;  shell  structure  finely  punctate. 

Remarks.— This  species  has  frequently  been  misinterpreted,  and 
tbree  or  more  distinct  species  belonging  to  three  different  genera  have 
commonly  been  known  under  this  name.  So  far  as  it  has  been  observed 
the  species  is  always  a  small  and  rather  gibbous  form,  but  it  varies  greatly 
in  its  gibbosity  and  also  in  the  development  of  the  concentric  lines  of 
growth,  the  more  gibbous  examples  commonly  being  most  strongly 
marked  by  growth  lines.  The  species  differs  from  G.  indianensis,  the  type 
of  the  genus  Girtyella,  in  its  shorter  shell  with  more  gibbous  and  usually 
less  smooth  valves,  and  in  the  much  more  conspicuous  sinus  of  the 
brachial  valve.  , 

Horizon. — Salem  limestone. 


GIRT V ELLA  lib 

GlRTYEI.LA    INDIANENSIS     (Girty) 

Plate  XXXIV,  Figs.  1-24 

L891.     Terebratula  turgida  Whitfield,  Ann.  N.  Y.  Acad.  Sei.,  vol.  5,  p.  586, 

pi.  13;  figs.  21-22. 
1895.     Terebratula  turgida  Whitfield.  Geol.  Surv.  Ohio.  vol.  7,  p.  473,  pi.  9, 

figs.  21-22. 
1908.     limit ina  indianensis  Girty,  Proc.  U.  S.  Xat.  Mus.   vol.  34,  p.  293, 

pi.  1!).  figs.  6-15. 
1911.     Dielasma  turgida  .Morse,  Proc.  Ohio  Acad.  Sei..  vol.  5,  p.  381,  figs. 

12a-b. 
1911.     Girtyella  indwrn  nsis  Weller,  Jour.  Geol.,  vol.  19.  p.  442,  figs.  2a-i. 

Description.  —  Shell  small,  longitudinally  subovate.  often  approaching 
subpentagonal  in  outline,  the  greatest  width  a  little  in  front  of  the  middle, 
the  anterior  margin  straightened  or  a  little  emarginate.  The  dimensions 
of  two  complete  examples  are:  Length  of  pedicle  valve  13  mm.  and  11.7 
mm.,  length  of  brachial  valve  12  mm.  and  10.4  mm.,  width  10.2  mm.  and 
9.5  mm.,  thickness  8  mm.  and  6  mm. 

Pedicle  valve  most  convex  near  or  a  little  posterior  to  the  middle, 
the  surface  curving  abruptly  towards  the  posterolateral  margins  and 
becoming  a  little  inflected  to  the  cardinal  extremities,  curving  less  ab- 
ruptly to  the  antero  lateral  and  anterior  margins;  mesial  sinus  obsolete 
in  the  umbonal  region,  rarely  originating  posterior  to  the  middle,  often 
being  confined  to  the  anterior  third  or  fourth  of  the  valve,  shallow, 
rather  narrow,  rounded  in  the  bottom  and  ill-defined  laterally;  the  beak 
rather  prominent  and  projecting  well  beyond  that  of  the  opposite  valve, 
incurved,  pierced  by  a  large,  longitudinally  elliptical  or  subovate  fora- 
men which  encroaches  in  its  entirety  upon  the  umbonal  portion  of  the 
valve ;  the  delthyrium  and  deltidial  plates  not  visible  externally  because 
of  the  incurvature  of  the  beak.  Internally  the  dental  lamellae  are  well 
developed  and  extend  nearly  one-fourth  the  length  of  the  valve  an- 
teriorly from  the  beak  with  a  moderate  degree  of  divergence. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity at  or  near  the  middle,  the  surface  curving  rather  abruptly  to  the 
postero-Iateral  margins,  arched  from    beak    to    front    with    the    curvature 

B  C  o 

Fig.  33. — A  series  of  four  cross-sections  of  the  rostral  portion  of  the  brachial  valve 
of  Girtyella  indianensis  (X  2%)  from  the  Renault  formation,  showing  the 
median  septum  and  concave  hinge-plate. 

often  a  little  more  abrupt  anteriorly;  a  mesial  fold  to  correspond  with 
the  sinus  of  the  opposite  valve  is  rarely  developed,  when  present  it  is 
narrow  and  obscure  with  a  slight  depression  on  either  side  and  orig- 
inates near  the  anterior  margin,  more  commonly  the  median  portion  of 


276  MISSISSIPPIAN   BRACHIOPODA 

tlic  valve  is  not  differentiated  a1  all,  or  an  obscure  sinus  is  present  anter- 
iorly, which,  meeting  the  sinus  of  the  opposite  valve,  produces  a  slight 
(■marginal  ion  of  the  shell ;  the  beak  pointed,  closely  incurved  beneath  that 
of  the  opposite  valve.  Internally  a  small,  obscure,  bilobed  cardinal 
process  is  present  at  the  apex  of  the  valve,  the  dental  sockets  are  formed 
by  well-defined  sockel  plates  which  are  united  by  an  imperforate,  concave 
binge-plate,  BUpported  by  a  median  septum,  anteriorly  the  socket  plates 
ret  real  from  the  margins  of  the  valves  and  are  transformed  into  the 
bases  of  the  crura   which   are  still  joined   by   the  concave  hinge-plate  and 

are  connected  also  with  the  inner  surfaces  of  the  Lateral  slopes  of  the 
valve;  the  median  septum  continues  anteriorly,  sometimes  to  near  the 
middle  of  the  valve,  after  it  has  become  I'yrt'  from  the  hinge-plate;  the 
brachidium  short,  not  reaching  the  middle  of  the  valve. 

Surface  of  both  valves  smooth  except  for  some  concentric  lines  of 
growth  which  vary  in  strength  and  number  in  different  individuals,  some- 
times being  practically  absent  and  again  being  well  developed.  Shell 
structure  finely  punctate. 

Remarks. — This  species  occurs  in  abundance  in  the  Pella  beds  of  Iowa 
and  elsewhere.  It  lias  usually  been  identified  as  Dielasma  turgida  and  only 
recently  has  been  described  as  a  dislinct  species  by  Girty  under  the  name 
Harttina  indianensis.  It  was  placed  in  the  genus  Harttina  on  account  of 
the  median  septum  of  its  brachial  valve,  but  its  brachidium  is  short  like 
that  of  Dielasma  and  it  cannot,  therefore,  be  considered  as  Harttina,  which 
has  an  elongate  brachidium  similar  to  that  of  Cryptonella.  The  combina- 
tion of  the  short  brachidium  and  the  hinge-plate  supported  by  a  median 
septum  has  not  hitherto  been  recognized  as  of  generic  value,  but  it  is  a 
stage  of  development  essentially  different  from  that  of  Dielasma,  present 
in  several  well-defined  species  and  is  deemed  to  be  worthy  of  recognition 
as  of  generic  value. 

The  species  differs  from  G.  turgida  in  its  more  elongate  form,  less 
gibbous  valves  and  in  the  usual  absence  or  obsolesence  of  any  median 
depression  of  the  brachial  valve. 

Horizom. — Ste.   Genevieve  limestone   and  Chester  Group. 

GlRTYELLA  INTERMEDIA  n.  sp. 

Plate  XXXIV,  Figs.  42-47 

Description. — Shell  small,  ovate-subpentagonal  in  outline,  the  anterior 
margin  truncate  or  a  little  emarginate,  the  greatest  width  near  or  a 
little  anterior  to  the  middle.  The  dimensions  of  two  nearly  complete 
specimens  are :  length  of  pedicle  valve  13.8  mm.  and  13.3  mm.,  length 
of  brachial  valve  12  mm.  and  11.5  mm.,  greatest  width  9.6  mm.  and  9.9 
mm.,  thickness  10  mm.  and  8.5  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  strongly  towards  the  postero-lateral  margins 


GIRTVELLA 


277 


iind  inflected  to  the  cardinal  extremities,  the  curvature  more  or  less 
abrupt  to  the  antero-lateral  margins;  mesial  sinus  well  developed,  rather 
narrow,  rounded  or  flattened  in  the  middle,  variable  in  depth,  originating 
posterior  to  the  middle  of  the  valve  sometimes  well  up  on  the  umbo,  its 
middle  portion  usually  slightly  produced  in  front  in  a  short  rounded 
extension ;  the  beak  prominent,  strongly  incurved,  the  foramen  large, 
subovate,  encroaching  wholly  upon  the  umbo.  Internally  the  dental 
plales  are  well  developed  and  elongate,  reaching  anteriorly  from  the  beak 
for  one-fourth  or  more  than  one-fourth  the  length  of  the  valve. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
the  middle,  the  surface  curving  abruptly  to  the  lateral  margins;  the 
mesial  portion  of  the  valve  somewhat  flattened  posteriorly  and  more 
broadly  flattened  or  slightly  depressed  in  a  shallow  mesial  sinus  in  front, 
near  the  front  margin  in  the  middle  of  the  sinus  or  flattened  region,  is  a 
narrow,  rounded  fold  or  plication  which  is  variable  in  the  strength  of 
its  development,  when  strongly  developed  in  association  with  the  rather 
narrowly  rounded  elevations  at  the  sides  of  the  sinus,  it  gives  to  the 
valve  a  marked  triplicate  appearance  in  front ;  the  beak  pointed  and 
incurved  beneath  that  of  the  opposite  valve.  Internally  the  socket 
plates  are  joined  by  the  concave  hinge-plate  which  is  supported  by  a 
median  septum,  the  crural  lamella'  are  not  distinct  from  the  socket  plates, 
the  free  descending  lamellae  of  the  brachidium  being  processes  from  the 
anterior  extremity  of  the  hinge-plate;  the  median  septum  is  elongate  and 
reaches  anteriorly  about  two-fifths  the  length  of  the  valve  from  the 
beak. 

Surface  of  both  valves  marked  only  by  concentric  lines  of  growth  which 
are  usually  obsolete  posteriorly  and  are  frequently  obscure  anteriorly. 
The  shell  structure  finely  punctate. 

Remarks. — The  more  extreme  specimens  of  this  species  are  strikingly 
like  examples  of  Dielasma  i)tflata  in  the  triplicate  anterior  extremity  of 
the  brachial  valve,  but  they  differ  fundamentally  from  that  species  in  the 
internal  characters  of  the  rostral  portion  of  the  brachial  valve,  besides 
having  the  convex  curvature  of  the  valves  more  regular  than  in  that 
species,  the  abrupt  geniculation  of  the  valve  being  absent.  As  compared 
with  other  species  of  Girtyella  this  one  is  essentially  intermediate  in  char- 
acter between  G.  turgida  and  G.  brevilubata.  It  has  the  strongly  convex 
valves  of  G.  turgida  but  lacks  the  broad,  rounded  sinus  of  the  brachial 
valve  which  is  so  characteristic  a  feature  of  that  shell,  and  has  the 
narrow,  rounded,  mesial  plication  of  the  same  valve  more  constantly 
present  and  more  strongly  developed.  In  this  last  feature  the  species  is 
more  nearly  like  G.  brevilobata,  but  it  is  a  shorter  shell  with  more  strongly 
convex  valves  than  that  species. 

Horizon.  —  Chester  Group,  Paint  Creek  formation. 


278  MISSISSIPPIAN    BBACHIOPODA 

GlBTYELLA    BREVILOBATA  Swallow 

Plate  XXXIV,  Pigs.  37-4] 

L863.     Terebratula  brevilobata  Swallow,  Trans,  St.  Louis  Acad.  Sei.,  vol. 

2,  p.  84. 
L894.     Dielasma  turgida  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pi.  :>:{,  fig.  in  mot  figs.  11-12). 
1895.     Dielasma  turgida  Ball  and  Clarke,  Pal.  X.  V.,  vol.  8,  pt.  2,  pi.  81, 

figs.  7-8  (  not  figs.  1-6). 
1897.     Dielasma  turgida  var.  <l<>n</<ihi  Weller,  Trans.  X  .V.  Acad.  Sei.,  vol. 

16,  \>.  260,  pi.  IS.  fig.  (i. 
1911.     Harttina  bn  vilobata  Girty,  'Bull.  I'.  S.  Geol.  Survey  No.  439,  p.  65, 

pi.  2.  fig.  12. 
Hill.     Oirtyella  brevilobata  Weller,  -lour.  Geol.,  vol.  19,  p.  443. 

Description. — Shell  small,  longer  than  wide,  subpentagonal  or  subovate 
in  outline,  the  greatest  width  near  the  mid-length,  the  anterior  margin 
truncated  or  more  usually  emarginate.  The  dimensions  of  a  nearly  per- 
fect example  are:  length  of  pedicle  valve  12.5  mm.,  length  of  brachial 
valve  11.2  mm.,  width  10  mm.,  thickness  7.5  mm. 

Pedicle  valve  most  convex  posterior  to  or  near  the  middle,  the  surface 
curving  abruptly  to  the  antero-lateral  margins,  becoming  inflected  to  the 
cardinal  margins,  curving  more  gently  to  the  antero-lateral  and  anterior 
margins;  mesial  sinus  usually  well  developed,  originating  near  the  urn- 
bona!  region,  narrow,  rounded  in  the  bottom,  becoming  rather  deep  ante- 
riorly ;  the  beak  rather  pointed,  projecting  notably  beyond  that  of  the 
opposite  valve,  incurved,  pierced  by  a  subovate  or  subelliptical  foramen 
which  encroaches  entirely  upon  the  umbonal  region  of  the  valve;  the  del- 
thyrium  and  deltidial  plates  bidden  by  the  incurvature  of  the  beak.  In- 
ternally the  dental  lamellae  are  well  developed  and  extend  anteriorly  with 
moderate  divergence  for  one-fourth  or  a  little  more  than  one-fourth  the 
length  of  the  valve. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  convex- 
ity near  the  middle,  the  surface  arched  from  beak  to  front  with  the  pos- 
terior slope  a  little  more  abrupt,  curving  abruptly  to  the  lateral  margins; 
at  a  point  from  one-third  to  one-fourth  the  length  of  the  valve  from  the 
anterior  margin  a  rather  broad  mesial  sinus  or  depression  originates, 
along  the  median  line  of  which  is  a  narrow,  rounded  fold,  somewhat  nar- 
rower than  the  sinus  of  the  opposite  valve,  giving  to  the  valve  a  distinctly 
trilobate  contour  with  the  median  lobe  smaller  than  the  two  outer  ones 
and  a  little  depressed  between  them ;  the  beak  pointed,  strongly  incurved 
beneath  that  of  the  opposite  valve.  Internally  the  socket  plates  are  con- 
nected by  a  slightly  concave  hinge-plate  which  is  suppoi'ted  by  a  median 
septum. 

Surface  of  both  valves  smooth  and  unornamented  except  by  concentric 
lines  of  growth  which  vary  in  the  strength  of  their  development  in  differ- 
ent individuals.     Shell  structure  finely  punctate. 


DIELASMELLA  279 

Remarks. — The  original  description  of  this  species  is  short  and  unac- 
companied by  illustrations,  and  the  type  specimen  is  believed  to  be  lost, 
but  the  definition  agrees  so  closely  with  the  shell  here  illustrated  that  the 
identification  is  believed  to  be  beyond  question. 

In  size  and  convexity  of  the  valves  this  species  resembles  G.  indianensis, 
but  it  differs  from  that  species  in  its  somewhat  more  pentagonal  outline, 
with  the  greatest  width  nearer  the  mid-length  of  the  shell,  and  especially 
in  the  deeper,  longer,  and  altogether  more  conspicuous  mesial  sinus  of  the 
pedicle  valve  and  the  short,  broad  sinus  of  the  brachial  valve  with  its  dis- 
tinct mesial  fold  or  plication.  This  trilobation  of  the  anterior  margin  of 
the  brachial  valve  is  sometimes  faintly  suggested  in  examples  of  G.  indian- 
<  nsis,  but  it  is  never  a  conspicuous  feature  as  in  this  species.  The  species 
differs  from  G.  turgida,  with  which  it  has  sometimes  been  identified,  in  its 
more  elongate  form  and  the  less  gibbosity  of  the  valves,  the  trilobation  of 
the  anterior  portion  of  the  brachial  valve  is  also  a  much  more  conspicuous 
feature,  although  that  character  is  not  infrequently  present  in  G.  turgida. 
The  shell  described  as  Dielasma  turgida  var.  elongata  Weller,  is  apparently 
a  member  of  this  species,  the  type  specimen  is  an  internal  cast  in  which 
the  median  septum  of  the  brachial  valve  is  clearly  seen,  it  is  proportion- 
ally a  little  narrower  and  consequently  more  slender  than  is  usual  among 
typical  representatives  of  G.  brevildbata,  but  it  possesses  the  long  median 
sinus  of  the  pedicle  valve  and  the  trilobation  of  the  front  of  the  brachial 
valve,  although  the  trilobation  is  somewhat  obscured  by  a  slight  distortion 
of  the  shell. 

Horizon. — Chester  group. 

Genus  DIELASMELLA  Weller 

Description. — Shell  terebratuliform,  compressed.  Pedicle  valve  with 
well  developed  dental  lamellae  of  moderate  length.  Brachial  valve  with- 
out median  septum  or  true  hinge-plate,  the  socket  plates  well  developed, 
retreating  from  the  lateral  margins  of  the  valve  anteriorly  and  becoming 
differentiated  into  two  portions,  a  basal    portion    which    joins  the  inner 


Fig.  34. — A  series  of  six  cross-sections  of  the  rostral  portion  of  the  brachial  valve  of 
Dielasmella  compressa  (X  2%),  showing  the  development  of  the  crura  from 
the  inner  walls  of  the  hinge  sockets,  and  the  narrow  band  joining  the  bases 
of  the  crura  just  before,  and  at  the  point,  where  they  become  free. 

surface  of  the  valve  and  is  directed  obliquely  inward,  and  a  distal  portion 
which  is  abruptly  bent  in  a  subgeniculate  angle  so  as  to  be  directed 
obliquely  outward,  the  portion  included  in  the  angular  bend  of  the  two 
plates  is  produced  anteriorly  into  the  bases  of  the  crura,  and  just  before 


280  MISSISSIPPIAN    BRACHIOPODA 

the  crura  become  free  a  narrow  transverse  hand  joins  their  liases.  The 
characters  of  the  brachidium  not  completely  determined,  but  it  is  clearly 
of  the  short,  Dielasma-like  type.     Shell  structure  finely  punctate. 

Remarks. —  In  the  arrangement  of  the  internal  features  of  the  apical 
portion  of  the  brachial  valve  this  genus  is  perhaps  more  closely  allied  to 
('mint mi  than  to  any  other  of  the  generic  types  here  recognized.  It  differs 
Erom  Cravuena  chiefly  in  the  reduction  of  the  hinge-plate  to  a  narrow  trans- 
verse hand  joining  the  crural  hases,  while  in  ('r«ii(ina  it  is  elongate  with  a 
comparatively  small  apical  perforation  and  with  the  crura  originating  as 
a  pair  of  ribs  diverging  anteriorly  from  near  the  apex.  The  difference  in 
shape,  viz:  the  much  compressed  shell  and  the  erect  beak  of  the  pedicle 
valve  are  other  features  which  easily  separate  the  members  of*  this  genus 
from  all  the  recognized  species  of  Cranium. 

DlELASMELLA   COMFRESSA    Weller 

Plate  XXX,  Pigs.  43-55 

1906.     Eunella   COmpressa    Weller,    Trans.    St.    Louis   Acad.    Sci.,    vol.    16, 

p.  442,  pi.  6,  figs.  13-16. 
1911.     Diclasmella  compressa  Weller,  Jour.  Geo].,  vol.  19,  p.  447,  figs.  7a-f. 

Description. — Shell  very  small,  lenticular,  compressed,  subovate  in  out- 
line, usually  longer  than  wide  hut  sometimes  a  little  wider  than  long,  the 
greatest  width  near  the  mid-length  of  the  shell.  The  dimensions  of  two 
complete  specimens  are:  length  of  pedicle  valve  5.9  mm.  and  6  mm.,  length 
of  brachial  valve  5.1  and  5.5  mm.,  width  5  mm.  and  6.5  mm.,  thickness  2 
mm  and  2.5  mm. 

Pedicle  valve  depressed  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  usually  very  gently  convex  towards  the  lateral  mar- 
gins but  sometimes  a  little  compressed  antero-laterally.  near  the  postero- 
lateral margins  the  surface  is  abruptly  inflected  to  the  cardinal  extremi- 
ties ;  the  median  portion  of  the  valve  differentiated  from  the  lateral  slopes 
as  a  narrow,  somewhat  ill-defined,  flattened  region  which  is  sometimes 
slightly  depressed  medially  in  a  faint  sinus;  the  beak  pointed,  nearly 
erect,  pierced  by  a  subcircular  foramen  which  only  partially  encroaches 
upon  the  umbonal  portion  of  the  valve ;  delthyrium  closed  by  a  pseudo- 
deltidium  except  in  its  apical  portion  wdiich  is  a  part  of  the  foramen. 
Internally  the  dental  lamella3  are  well  developed  and  are  of  moderate 
length. 

Brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  surface  with  a  nearly 
straight  slope  along  the  median  line  from  the  middle  of  the  valve  to  the 
front,  convexly  curved  to  the  beak,  the  lateral  slopes  very  gently  convex 
and  sometimes  a  little  compressed  towards  the  cardinal  extremities;  the 
median  portion  of  the  valve  differentiated  as  a  rather  narrow,  flattened 


DIELASMELLA  281 

region  similar  to  that  of  the  opposite  valve;  the  beak  pointed,  incurved 
beneath  the  base  of  the  pseudodeltidinm  of  the  opposite  valve.  Internally 
the  characters  are  in  accord  with  the  description  of  the  generic  characters 
already  given. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  fine,  obscure, 
concentric  lines  of  growth.     Shell  structure  finely  punctate. 

Remarks. — This  little  species  was  originally  described  as  a  member  of 
the  genus  Eunella.  It  agrees  with  Eunella  in  having  a  short  brachidium, 
but  it  has  not  been  possible  to  determine  whether  the  loop  is  of  the 
Eunella  type,  viz:  with  subparallel  descending  lamellae,  or  whether  it  re- 
sembles the  Dielasma  loop  in  which  the  descending  lamellae  are  divergent. 
Eunella,  however,  is  defined  as  having  a  distinct  hinge-plate  similar  to  that 
of  Cryptonella  or  Cranana,  while  in  this  species  no  true  hinge-plate  is 
present,  as  has  been  pointed  out  in  the  definition  of  the  genus,  the  trans- 
verse connection  between  the  bases  of  the  crura  being  reduced  to  a  narrow 
band. 

Horizon. — Glen  Park  limestone  of  the  Kinderhook. 

DIELASMELLA  CALHOUNENSIS  n.  sp. 

Plate  XXXI,  Figs.  1-4 

Description. — Shell  small,  compressed,  lenticular,  subovate  to  ovate- 
subpentagonal  in  outline,  longer  than  wide  or  sometimes  about  as  long 
as  wide,  the  greatest  width  near  or  a  little  anterior  to  the  middle.  The 
dimensions  of  a  nearly  complete  specimen  are :  length  of  pedicle  valve 
10.5  mm.,  length  of  brachial  valve  9.5  mm.,  greatest  width  8.5  mm.,  thick- 
ness 4  mm. 

Pedicle  valve  depressed  convex,  the  greatest  convexity  near  the  umbo, 
the  surface  nearly  flat  or  gently  convex  towards  the  lateral  margins, 
abruptly  inflected  along  the  postero-lateral  margins  to  the  cardinal  ex- 
tremities ;  the  mesial  portion  of  the  valve  slightly  flattened  along  an  in- 
definite, rather  narrow  band  from  in  front  of  the  umbonal  region  to  the 
anterior  margin  and  frequently  depressed  along  the  median  line  of  this 
band  in  a  shallow  but  distinct  median  sinus ;  beak  pointed,  nearly  erect, 
pierced  by  a  subcircular  foramen  which  encroaches  largely  upon  the  um- 
bonal portion  of  the  valve,  only  the  margin  being  included  in  the  delthy- 
rium ;  the  delthyrium  entirely  closed  by  deltidial  plates  except  at  its  apex, 


B 

Fig.  35. — A  series  of  seven  cross-sections  of  the  rostral  portion  of  the  brachial 
valve  of  Diclasmclla  calhounensis  (X  2%),  showing  the  development  of  the 
crural  lamellae  from  the  inner  walls  of  the  hinge  sockets,  and  the  narrow  band 
joining  the  bases  of  the  crura  just  before  they  become  free. 


282  MIssissiiTI AN    BRACHIOPODA 

which  is  included  in  the  foramen.  Internally  the  dental  lamella-  are  well 
developed  and  of  moderate  Length,  their  anterior  extremities  sometimes 
curving  inward  towards  the  median  line  of  the  valve. 

Brachial  valve  a  little  more  convex  than  the  pedicle,  the  greatesl  con- 
vexity posterior  to  the  middle,  the  surface  curving  somewhat  abruptly 
from  the  umbonal  region  to  the  cardinal  extremities  and  more  gently  to 
the  lateral  and  anterior  margins;  the  mesial  portion  of  the  valve  flattened 
in  a  similar  manner  to  the  flattening  of  the  opposite  valve  and  not  in- 
frequently depressed  in  a  distinct  but  shallow  median  sinus;  the  beak 
pointed,  incurved  beneath  the  base  of  the  pseudodeltidium  of  the  opposite 
valve.  Internally  the  characters  tit'  the  apical  portion  of  the  valve  are  in 
accord  with  the  definition  of  the  genus  already  given;  the  complete  form 
of  the  brachidium  not  known. 

Surface  of  both  valves  nearly  smooth,  only  marked  by  concentric  lines 
of  growth  which  are  frequently  rather  strong  and  crowded  towards  the 
anterior  margin.    The  shell  structure  finely  punctate. 

Remarks  -This  species  is  a  close  ally  of  D.  compressa  and  perhaps 
should  not  be  separated  from  it.  It  is  always  a  larger  form,  however, 
with  the  brachial  valve  relatively  more  convex  and  with  the  median  sinus 
of  the  pedicle  valve  more  conspicuously  developed.  No  examples  have 
been  observed  in  which  the  width  exceeds  the  length,  as  sometimes 
happens  in  the  smaller  species,  and  the  concentric  growth  lines  are  more 
strongly  developed  than  in  D.  compressa.  Most  or  all  of  these  differential 
characters  might  perhaps  be  accounted  for  in  the  larger  size  of  the  indi- 
viduals of  D.  calhouvt  nsis,  but  for  the  present,  at  least,  the  two  forms  will 
be  considered  as  distinct.  In  the  internal  characters  of  the  brachial  valve 
upon  which  the  genus  is  established,  the  two  forms  are  essentially  identi- 
cal, the  only  difference  being  due  to  the  greater  compression  of  the  valve 
in  D.  compressa. 

Horizon. — Hamburg  oolite  of  the  Kinderhook. 

Genus  HAMBVBGIA  Weller 

Description. — .Shell  terebratuliform,  with  well  developed  dental  lamella? 
in  the  pedicle  valve.  The  brachial  valve  without  cardinal  process  other 
than  the  slight  thickening  of  tht  shell  margin  at  the  apex  of  the  valve, 
the  socket  plates  well  developed,  retreating  from  the  lateral  margins  of 
the  valve  anteriorly  beyond  the  articulation  of  the  valves,  and  connected 
transversely  by  a  deeply  concave  hinge-plate  which  is  separated  from 
the  inner  surface  of  the  valve  by  an  exceedingly  low  and  broad  cavity; 
upon  the  inner  or  concave  side  of  the  hinge-plate  a  pair  of  ridges  orig- 
inate towards  the  apex  and  diverge  slightly  while  becoming  stronger 
anteriorly,  finally  passing  into  the  bases  of  the  crura  ;  shortly  in  front 
of  tbe  point  of  origin  of  the  crural  ridges  on  the  binge-plate  the  socket 


IIA.AIRI'RGIA 


283 


plates  are  rapidly  reduced  in  height  and  soon  become  obsolete,  beyond 
which  point  the  hinge-plate  is  not  connected  with  the  inner  surface  of 
the  valve,  but  becomes  a  concave  plate  joining  the  bases  of  the  crura 
and  terminating  anteriorly  in  a  short  distance.  The  complete  form  of  the 
brachidium  is  not  known,  but  it  is  probably  short,  not  reaching  the 
mid-length  of  the  valve. 

Bema/rks.  —  This  genus  is  perhaps  most  closely  allied  to  Crancena,  from 
which  it  differs  in  the  extreme  concavity  of  the  hinge-plate,  the  cavity 
between  it  and  the  inner  surface  of  the  valve  being  nruch  reduced  in 
height;  accompanying  the  great  depression  of  the  hinge-plate  is  the 
absence  of  its  perforation  at  the  apex,  which  is,  perhaps,  the  most  diagnos- 
tic character.  The  genus  is  totally  distinct  from  Dielasma,  in  which  the 
crural  plates  originate  as  ridges  upon  the  inner  surface  of  the  valve 
instead  of  upon  the  concave  surface  of  the  hinge-plate;  the  concave  trans- 
verse plate  between  the  bases  of  the  crura  is  somewhat  similar  in  the 
two  genera  except  that  it  is  not  connected  along  its  median  line  to  the 
inner  surface  of  the  valve  in  Hamburgia,  but  in  Dielasma  the  inner  surface 
of  this  plate  furnishes  attachment  for  the  adductor  muscles  which  ap- 
parently is  not  true  in  Hamburgia. 

Hamburgia  typa  Weller 

Plate  XXXI,  Figs.  16-18 

1906.     Cryptonella   1  sp.  undet.  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol. 

16,  p.  443. 
1911.     Hamburgia  typa  Weller,  Jour.  Geol.,  vol.  19,  p.  446,  figs.  6a-h. 

Description. — Shell  below  medium  size,  subovate  in  outline,  longer  than 
wide,  the  greatest  width  near  the  mid-length,  the  postero-lateral  margins 
nearly  straight  or  gently  convex,  the  antero-lateral  and  anterior  margins 
semicircular.  The  dimensions  of  two  detached  pedicle  valves  are :  length 
17.8  mm.  and  15.8  mm.,  width  14.8  mm.  and  12  mm.,  convexity  4.7  mm. 
and  4.4  mm.  The  dimensions  of  a  brachial  valve  are:  length  14  mm., 
width  11.9  mm.,  convexity  4.4  mm. 

Pedicle  valve  with  the  greatest  convexity  near  or  a  little  posterior  to 
the  middle,  the  surface  arched  from  beak  to  front  along  the  median  line 
either  nearly  symmetrically  or  with  a  slightly  increasing  convexity  pos- 
teriorly, the  slope  gently  convex  from  the  median  line  to  the  lateral  mar- 
gins, becoming  a  little  inflected  towards  the  cardinal  extremities ;  mesial 
sinus  obsolete,  but  the  mesial  portion  of  the  valve  is  sometimes  slightly 
flattened  along  an  indefinite  band;  beak  truncated,  not  strongly  incurved, 
with  a  large,  subcircular  foramen  which  encroaches  wholly  upon  the  urn- 
bonal  region,  only  the  apex  of  the  delthyrium  being  in  contact  with  it; 
the  delthyrium  broadly  triangular,  completely  closed  by    a    pseudodel- 


284  MISS1SSIPPIAN    BRACHIOPODA 

tidium  except  where  it  is  filled  by  the  incurved  beak  of  the  opposite  valve. 
Internally  the  dental  lamella'  are  well  developed  and  extend  anteriorly 
from  the  beak  for  about  one-fourth  the  length  of  the  valve. 

Brachial  valve  nearly  equally  or  a  little  less  convex  than  the  pedicle, 
the  greatest  convexity  near  or  a  little  posterior  to  the  middle,  the  snrface 
arched  from  the  beak  to  the  front  with  the  convexity  a  little  greater  pos- 


Fig.  36. — A  series  of  nine  cross-sections  of  the  umbonal  region  of  the  brachial 
valve  of  Hamburgia  typa  (X  2%),  showing  the  development  of  the  deeply 
concave  hinge-plate,  with  the  crural  ridges  upon  it. 

teriorly,  the  lateral  slopes  convex,  curving  regularly  from  the  median 
line  to  the  lateral  margins,  the  curvature  being  more  abrupt  posteriorly; 
mesial  portion  of  the  valve  not  differentiated  from  the  general  convexity; 
the  beak  pointed,  incurved  beneath  that  of  the  opposite  valve.  Internally 
the  characters  are  in  accordance  with  the  generic  description  already 
given. 

The  snrface  of  both  valves  is  commonly  marked  by  well-defined,  concen- 
tric lines  of  growth  which  vary  in  different  individuals  in  number  and 
distribution.     Shell  structure  minutely  punctate. 

Remarks. — This  species  is  a  common  one  in  the  fauna  of  the  Kinderhook 
oolite  at  Hamburg,  Illinois,  and  occurs  also  in  the  Glen  Park  limestone  of 
Missouri.  It  resembles  several  species  of  Mississippian  terebratuloid 
shells  in  which  the  fold  and  sinus  are  obsolete,  but  perhaps  agrees  more 
closely  in  external  form  with  Dielasma  chouteauense  than  with  any  other. 
It  may  be  distinguished  from  that  species,  however,  by  the  less  incurved 
beak  of  the  pedicle  valve  which  is  distinctly  truncated,  and  usually  by 
the  more  numerous  and  stronger  concentric  lines  of  growth.  The  internal 
characters  of  the  rostral  portion  of  the  brachial  valve  are  totally  differ- 
ent, however,  in  these  two  species,  and  they  are  not  even  members  of  the 
same  genus. 

Horizon. — Hamburg  oolite  and  Glen  Park  limestone  of  the  Kinderhook. 

Family  ATRYPID.E 
Genus  ATRYPA  Dalman 

Description.— Shell  subcircular  in  outline,  strongly  inequivalved  with 
the  brachial  valve  gibbous  or  with  the  valves  snbequally  convex,  the 
hinge-line  short  and  the  cardinal  extremities  rounded,  surface  radially 
plicate  and  usually  marked  also  by  more  or  less  conspicuous,  concentric. 


ATRYPA  285 

lamellose  lines  of  growth.  Pedicle  valve  with  a  small,  incurved  beak 
with  the  foramen  and  delthyrium  hidden  except  in  young  individuals; 
internally  the  hinge-teeth  are  large  and  widely  separated,  and  the 
muscular  impressions  are  sharply  defined.  In  the  brachial  valve  the 
crura  are  long,  narrow  and  widely  divergent,  the  jugum  consists  of  two 
processes  situated  posteriorly  at  the  junction  of  the  crura  with  the 
primary  Lamellae,  directed  towards  the  center  of  the  shell  and  not  joined 
at  their  inner  extremities,  the  spirals  have  their  bases  subparallel  with 
the  inner  surface  of  the  pedicle  valve,  with  their  apices  convergent 
towards  the  center  of  the  brachial  valve. 

Remarks.— The  genus  Atrypa  is  commonly  considered  to  have  become 
extinct  at  the  close  of  Devonian  time,  but  it  does  persist  into  the  Missis- 
sippian  where  it  is  limited  to  the  Kinderhook  division  and  is  one  of  the 
rarest  members  of  the  fauna. 

Atrypa  infrequens  n.  sp. 
Plate  XXXV,  Figs.  1-5 

1906.     Atrypa  spinosa  Weller,  Trans.  St.  Louis  Acad.  Sei.,  vol.  16,  p.  443, 
pi.  6,  tig.  17. 

Description.  —  Shell  small,  lenticular,  subcircular  in  outline,  the  hinge- 
line  very  short.  The  dimensions  of  the  holotype  are:  length  of  pedicle 
valve  7  mm.,  length  of  brachial  valve  6.1  mm.,  greatest  width  7  mm.,  length 
of  hinge-line  3  mm.,  thickness  3.5  mm. 

Pedicle  valve  depressed-convex,  the  greatest  depth  posterior  to  the 
middle,  the  umbo  rather  prominent  with  the  surface  sloping  abruptly  to 
the  cardinal  margin,  and  curving  with  gentle  convexity  to  the  lateral  and 
anterior  margins ;  mesial  sinus  absent ;  the  beak  obtusely  pointed  and 
produced  posteriorly  beyond  the  hinge-line  nearly  in  line  with  the  plane 
of  the  valve,  only  slightly  incurved;  cardinal  area  small,  a  little  concave. 

Brachial  valve  a  little  less  concave  than  the  pedicle,  flattened  in  the 
umbonal  region  and  a  little  compressed  towards  the  cardinal  extremities, 
the  surface  curving  with  a  very  gentle  convexity  to  the  lateral  and  an- 
terior margins;  the  beak  inconspicuous,  scarcely  projecting  beyond  the 
hinge-line. 

Each  valve  marked  by  about  fifteen  rounded  plications,  a  very  few  of 
which  bifurcate  in  the  umbonal  region,  they  increase  regularly  in  size 
distally,  becoming  very  coarse  at  the  outer  margin  of  the  shell;  the  pli- 
cations are  crossed  by  strong,  regular,  concentric  lines  of  growth  which 
are  raised  as  lamellose  extensions  of  the  shell  upon  the  tops  of  the  pli- 
cations. 

Remarks. — This  little  shell  has  much  the  aspect  of  a  small  A.  spinosa 
from  the  Middle  Devonian,  and  was  originally  so  identified.     The  single 


286  \i  ississil'i'l.w    BRACHIOPODA 

specimen  which  1ms  conic  under  observation  is  apparently  an  adult  indi- 
vidual, judging  from  the  thickening  of  the  valves  at  their  free  margins, 
,-mil  is  many  times  smaller  than  adult  examples  of  the  Devonian  A,  spinosa. 
size  alone  would  perhaps  not  be  a  character  upon  which  a  species  could 
be  established,  bu1  in  addition  to  this  the  brachial  valve  is  considerably 
less  convex  than  the  pedicle,  while  in  .1.  spinosa  the  brachial  valve  is 
the  more  convex. 
Horizon. — Glen  Park  limestone  of  the  Kinderhook. 

Family  SPIRIPERIDJE 
Genus  CYRTINA   Davidson 

Description.  Shells  small,  semipyramidal  in  form,  with  usually  non-pli- 
cated mesial  fold  and  sinus,  and  simply  plicated  lateral  slopes.  Pedicle 
valve  with  ;i  high,  vertical  or  arched  cardinal  area  which  may  be  sym- 
metrical or  more  or  less  distorted,  the  delthyrium  narrowly  triangular, 
closed  with  a  convex  pseudodeltidium  which  is  perforated  at  a  point  be- 
low the  apex  by  a  subcircular,  direct  or  oblique  foramen,  or  may  be  with- 
out any  opening.  Internally  the  dental  lamella'  are  strongly  developed 
and  converge  rapidly  towards  the  inner  surface  of  the  valve,  before  meet- 
ing which  they  become  joined  in  a  single  median  septum  which  con- 
tinues to  the  floor  and  extends  anteriorly  beyond  the  center,  of  the 
valve.  Brachial  valve  very  shallow,  with  narrow,  inconspicuous  cardinal 
area.  Internally  the  cardinal  area  consists  of  a  double  apophysis  from 
the  sides  of  which  diverge  the  strong  crural  plates;  the  spiral  cones  are 
directed  obliquely  towards  the  middle  of  each  lateral  slope  of  the  pedicle 
valve,  the  jugum  is  continuous,  its  branches  being  directed  upward  and 
forward,  uniting  at  their  extremities.     Shell  substance  strongly  punctate. 

Remarks.— The  genus  Cyrtina  has  its  greatest  development  in  the  Devo- 
nian faunas,  being  represented  in  only  the  earlier  portion  of  Mississippian 
time.  It  differs  from  Spiriferina,  another  strongly  punctate  shell, 
in  the  union  of  the  dental  lamella?  to  form  a  spondylium  supported  by  a 
median  septum,  as  well  as  in  the  more  conspicuous  semipyramidal  form 
of  the  shell. 

Cyrtina  acutirostris  (Shumard) 
Plate  XXXV,  Figs.  6-21 

1855.     Cyrtia  acutirostris  Shumard,   Geol.   Rep.  Mo.,  p.   204.  pi.   C,  figs. 

3a-c. 
1894.     Cyrtina  acutirostris  Hall  and  Clarke,  Int.  to  Studv  of  Brach.,  pt.  2, 

pi.  29,  fig.  18. 

1894.  Cyrtina  acutirostris  Keyes,  Mo.  Geol.  Surv..  vol.  5.  p.  89,  pi.  39, 

figs.  lOa-b. 

1895.  Cyrtina  acutirostris  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  28, 

figs.  38-42,  44,  54. 


CYRT1NA  287 

1908.     Cyrtina  acutirostris  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 
2nd  ser.,  p.  84,  pi.  18,  figs.  16-20;  p.  87,  pi.  19,  fig.  2. 

Descript ion. — Shell  small,  subpyrarnidal  in  form,  broader  than  long,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  angular.  The 
dimensions  of  two  examples  are :  length  of  pedicle  valve  13.4  mm.  and 
7.3  mm.,  length  of  brachial  valve  8.2  mm.  and  6.2  mm.,  width  15.6  mm.  and 
11  mm.,  thickness  10  mm.  and  6.9  mm.,  height  of  cardinal  area  5.7  mm. 
and  5.1  mm. 

Pedicle  valve  subpyrarnidal  with  the  apex  nearly  erect  or  curved  to- 
wards the  hinge-line  in  various  degrees ;  the  surfaces  of  the  lateral  slopes 
unusually  convex  throughout  and  sloping  steeply  from  the  umbo  to  the 
lateral  and  antero-lateral  margins,  sometimes  a  little  compressed  along 
the  cardinal  margin  towards  the  cardinal  extremities ;  mesial  sinus  shal- 
low or  of  moderate  depth,  originating  at  the  beak,  rounded  or  subangular 
in  the  bottom ;  the  cardinal  area  high,  nearly  flat  in  the  younger  shells  and 
lying  at  an  angle  of  from  60  to  90  degrees  to  the  plane  of  the  valve,  re- 
maining nearly  flat  or  becoming  more  or  less  strongly  arched  in  full  grown 
shells,  the  lateral  margins  are  sharply  defined  and  angular,  and  slope  in 
nearly  straight  lines  or  are  gently  convex  from  the  beak  to  the  cardinal 
extremities;  the  delthyrium  is  high  and  narrow  and  is  covered  by  a  con- 
vex pseudodeltidium  which  is  pierced  by  an  elongate,  narrow  foramen 
sometimes  reaching  from  the  apex  more  than  half  way  to  the  cardinal 
margin ;  each  lateral  slope  is  marked  by  three  or  four  simple  plications 
originating  along  the  cardinal  margin,  the  two  bounding  the  mesial  sinus 
are  much  the  strongest,  the  others  rapidly  becoming  much  narrower  and 
weaker.  Internally  a  strong  median  septum  reaches  from  the  beak  half 
way  to  the  front  margin  of  the  valve,  towards  the  cardinal  area  the  septum 
is  flanked  by  the  rather  short  dental  plates  which  reach  from  the  margins 
of  the  delthyrium ;  in  the  angle  formed  by  the  junction  of  the  dental 
plates  with  the  median  septum  an  angular  ridge  extends  from  the  apex  of 
the  delthyrium  to  the  free  margin  of  the  septum  and  in  front  of  this  ridge 
between  the  laminae  of  the  septum  is  a  pair  of  laterally  compressed  canals 
placed  side  by  side  and  extending  from  near  the  apex  of  the  valve  to  the 
free  margin  of  the  septum ;  the  muscular  scars  are  feebly  developed,  and 
the  muscles  were  probably  attached  in  large  part  to  the  sides  of  the 
septum. 

Brachial  valve  depressed  convex,  very  shallow,  compressed  towards  the 
cardinal  extremities,  the  greatest  convexity  near  the  middle ;  the  mesial 
fold  low  or  sometimes  moderately  elevated  as  it  approaches  the  front 
margin,  non-plicate  or  with  a  slight  mesial  depression  which  is  sometimes 
present  only  towards  the  beak  ;  each  lateral  slope  marked  by  three  or  four 
plications,  the  first  of  which  adjacent  to  the  mesial  fold  is  nearly  as  broad 
as  the  fold  itself,  the  others  much  smaller,  the  last  one  often  being  nearly 


288 


MISSISSIPPIAN    r.UAcilloi'ODA 


obsolete;  the  cardinal  area  linear.  Internally  the  valve  is  thickened 
towards  the  cardinal  margin,  the  cardinal  process  is  bifid  and  from  it  a 
pair  of  crural  plates  or  ridges  diverge  anteriorly  and  curve  towards  the 
lateral  margins  of  the  valve  with  the  hinge  sockets  excavated  from  the 
sides;  the  muscle  sears  occupy  a  suboval  area  which  does  not  extend  lat- 
erally beyond  the  boundaries  of  the  mesial  Told  and  which  extends  ante- 
riorly to  beyond  the  middle  of  the  valve. 

Surface  of  both  valves  marked  by  rather  strong,  concentric  lines  of 
growth  which  are  frequently  crowded  at  intervals,  especially  towards  the 
front.     Shell  substance  finely  punctate. 

It<  marks. — This  is  one  of  the  most  characteristic  species  in  the  fauna 
of  the  Louisiana  limestone.  It  may  be  easily  distinguished  from  other 
members  of  the  genus  by  the  broad  plications  on  each  side  of  the  fold  and 
sinus.  On  the  brachial  valve  these  plications  are  frequently  nearly  as 
wide  as  the  mesial  fold  itself,  while  the  ones  beyond  are  much  narrower. 

Horizon. — Louisiana  limestone. 


Cyrtina  burlingtonensis  Rowley 
Plate  XXXV,  Figs.  22-31 

1893.     Crytina  burlingtonensis  Rowley,  Am.  Geo!.,  vol.  12,  p.  308,  pi.  14, 

figs.  15-17. 
1909.     Cyrtina  burlingtonensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p. 

310,  pi.  13,  figs.  20-23. 

Description. — Shell  small,  obliquely  suhpyramidal  in  form,  the  hinge- 
line  usually  a  little  shorter  than  the  greatest  width  of  the  shell,  and  the 
cardinal  extremities  a  little  rounded.  The  dimensions  of  two  nearly  per- 
fect specimens  are:  length  of  pedicle  valve  13.2  mm.  and  9.6  mm.,  length 
of  brachial  valve  9  mm.  and  6.7  mm.,  width  12.8  mm.  and  9.5  mm.,  thick- 
ness 9  mm.  and  6.5  mm.,  height  of  cardinal  area  5  mm  and  3.3  mm.,  length 
of  hinge-line  11.6  mm.  and  7.5  mm.  The  dimensions  of  the  holotype  are: 
length  of  pedicle  valve  10.5  mm.,  length  of  brachial  valve  7.5  mm.,  great- 
est width  11.1  mm.,  thickness  7.2  mm.,  height  of  cardinal  area  3.6  mm., 
length  of  hinge-line  8.5  mm. 

Pedicle  valve  very  deep,  obliquely  subpyramidal,  the  lateral  slopes  con- 
vex to  the  cardinal  extremities;  the  mesial  sinus  shallow  and  narrow,  orig- 
inating at  the  beak,  rounded  or  subangular  in  the  bottom;  the  beak  sharply 
pointed  and  incurved  over  the  cardinal  area ;  cardinal  area  high,  trian- 
gular, usually  strongly  arched  with  the  curvature  becoming  greater 
towards  the  beak,  the  lateral  margins  not  sharply  defined  but  rounding 
regularly  into  the  lateral  slopes  of  the  valve ;  the  delthyrium  high  and 
narrow,  covered  by  a  convex  pseudodeltidium  which  is  pierced  by  a 
rather  small,  longitudinally  subelliptical  foramen  situated  close  under  the 
beak,  or  in  some  cases  apparently  imperforate ;    each  lateral  slope  of  the 


CYRTINA  289 

valve  is  marked  by  three  or  four  rounded  plications  which  originate  at 
the  cardinal  margin,  the  two  plications  bounding  the  sinus  are  much  the 
stronger,  the  outermost  ones  becoming  much  less  distinct  and  sometimes 
nearly  obsolete.  Internally  a  strong  median  septum  readies  nearly  or 
quite  half  way  from  the  beak  to  the  front  margin. 

Brachial  valve  depressed  convex,  sometimes  nearly  flat,  compressed 
towards  the  cardinal  extremities ;  mesial  fold  rounded,  originating  at  the 
beak,  scarcely  elevated  above  the  plications  on  either  side ;  each  lateral 
slope  marked  by  two  or  three  plications,  the  outermost  ones  being  more  or 
less  indistinct.     Internal  characters  not  observed. 

Besides  the  plications  the  surface  of  both  valves  is  marked  by  concen- 
tric lines  of  growth  which  are  frequently  rather  strong  and  somewhat 
crowded  towards  the  front  margin.     Shell  structure  minutely  punctate. 

Remarks.— The  shell  which  has  been  identified  as  C.  burlingtonensis  oc- 
curs most  commonly  in  the  Chouteau  limestone  fauna.  It  differs  from 
C.  acutirostris  of  the  Louisiana  limestone  in  its  narrower  and  more  elongate 
form  with  more  attenuate  beak,  in  the  rounded  lateral  margins  of  the 
cardinal  area,  and  in  the  comparatively  narrower  plications  next  to  the 
mesial  fold  of  the  brachial  valve.  The  species  was  originally  described 
by  Rowley  from  the  white  cherts  at  the  base  of  the  Burlington  limestone 
at  Louisiana,  Missouri,  and  it  has  been  recognized  in  the  Fern  Glen  fauna. 

Horizon. — Chouteau  limestone,  Fern  Glen  formation  and  base  of  the 
Burlington  limestone. 

Cyrtina  neocenes  Hall  and  Clarke 
Plate  XXXV,  Figs.  32-38 

1895.     Cyrtina  sp.     .'    Hall  and  Clarke,  Pal.  X.  Y..  vol.  8,  pt.  2.  pi.  39, 

figs.  25-28. 

1895.     Cyrtina  neogenes  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2.  pi.  84, 

fig.  41. 
1897.     Cyrtina  neogenes  Hall.  14th  Rep.  N.  Y.  State  Geol.,  p.  372,  pi.  8, 
figs.  4-8. 

Description.  —  Shell  below  medium  size  or  small,  broader  than  long,  the 
hinge-line  shorter  than  the  greatest  width  of  the  shell,  the  cardinal  ex- 
tremities rounded.  The  dimensions  of  two  specimens  are:  length  of 
pedicle  valve  15  mm.  and  7.1  mm.,  length  of  brachial  valve  11  mm.  and 
6.5  mm.,  width  16.8  mm.  and  11  mm.,  thickness  14  mm.  and  6  mm.,  length 
of  hinge-line  13  mm.  and  8.7  mm.,  height  of  cardinal  area  5.5  mm.  and 
2.3  mm. 

Pedicle  valve  strongly  convex,  the  convexity  extending  out  to  the  car- 
dinal extremities;  the  mesial  sinus  sharply  defined,  non-plicate,  rather 
deep  and  of  moderate  width,  subangular  in  the  bottom ;  cardinal  area 
rather  high,  concave,  becoming  more  strongly  arched  towards  the  beak, 

—10 


L'ilO  MIssissii'i'lAN   BBACHIOPODA 

the  Lateral  margins  in  the  interna]  casts  rounding  regularly  into  the 
lateral  slopes  of  the  shell;  the  delthyrium  narrowly  triangular  with  no 
indication  of  deltidial  plates  iii  the  easts,  although  such  were  probably 
present  ;  each  lateral  slope  marked  by  from  six  to  eight,  simple,  rounded 
or  Bubangular  plications  which  originate  at  the  cardinal  margin,  be- 
coming regularly  less  conspicuous  laterally,  the  outermost  ones  some- 
times becoming  almost  obsolete.  Internally  a  strong  median  septum  ex- 
tends from  the  beak  half  way  to  the  anterior  margin,  the  dental  plates 
are  short  and  join  the  median  septum  to  form  a  spondylium.  muscular 
scars  obscure. 

Brachial  valve  less  convex  than  the  pedicle,  the  convexity  extending  out 
to  the  cardinal  extremities  and  greatest  near  the  middle;  mesial  fold  non- 
plicate,  rounded,  of  moderate  width,  bounded  by  deep  rounded  furrows, 
only  moderately  elevated  above  the  general  surface  of  the  valve;  each 
lateral  slope  marked  by  from  five  to  seven  simple,  rounded  plications 
entirely  similar  to  those  of  the  opposite  valve.  Internally  the  muscular 
scars  are  obscure,  the  only  marking  shown  upon  the  internal  casts  being 
a  slight  median  ridge  which  extends  from  the  beak  anteriorly  to  about 
the  middle  of  the  valve ;  the  cardinal  process  is  of  moderate  size  and  is 
Hanked  by  the  diverging  crural  plates. 

Besides  the  plications  the  surface  of  each  valve  is  marked  by  fine, 
regular,  sublamellose,  imbricating,  concentric  lines  of  growth,  about  three 
occupying  the  space  of  one  millimeter.  Shell  structure  thickly  and  rather 
coarsely  punctate,  the  perforations  being  arranged  in  the  central  portion 
of  the  valves,  and  perhaps  also  laterally,  in  regular  concentric  lines  cor- 
responding with  the  depressions  between  the  external  markings  of  the 
shell. 

Remarks.- — This  species  has  been  observed  only  as  internal  casts  and 
external  moulds,  from  residual  cherts  at  Springfield  and  elsewhere  in 
Missouri,  the  type  specimens  of  the  species  being  from  that  locality  rather 
than  from  Burlington,  Iowa,  as  stated  by  the  authors  of  the  species.  The 
proper  horizon  of  the  species  is  also  incorrectly  recorded  in  the  original 
description,  the  horizon  as  indicated  by  associated  species  in  the  cherts, 
being  as  high  as  Keokuk  rather  than  the  Burlington. 

In  its  general  form  and  surface  markings  the  species  resembles  some 
members  of  the  genus  Spiriferina  much  more  closely  than  other  members 
of  the  genus  Cyrtina.  It  especially  resembles  some  shells  from  the  Salem 
limestone  fauna  which  has  been  commonly  identified  as  Spiriferina  spinosa, 
but  it  has  a  little  less  angular  plications,  and  the  cardinal  margins  of  the 
pedicle  valve  are  not  sharply  defined,  but  round  regularly  from  the 
lateral  slopes  into  the  cardinal  area.  Internally  the  species  is  funda- 
mentally different  from  Spiriferina,  in  the  union  of  the  dental  plates  in  a 
spondylium  supported  by  a  median  septum.     The  punctate  shell  structure 


SI'IKIFKKIXA  291 

is  clearly  shown  in  the  chert  specimens  by  the  little  siliceous  pillars 
which  join  the  two  surfaces  of  the  cavity  left  by  the  solution  of  the 
shell,  these  pillars  being  the  casts  of  the  perforations  which  penetrated  the 
shell  through  its  entire  thickness,  unless  a  thin  epidermal  imperforate 
layer  was  removed  before  the  shells  were  fossilized. 
Horizon. — Residual  chert,  probably  Keokuk  age. 

Genus  SPIRIFERINA  d'Orbigny 

Description.— Shells  usually  small,  spiriferoid  in  form,  transverse,  the 
greatest  width  usually  along  the  hinge-line  and  the  cardinal  extremities 
acutely  angular;  mesial  fold  and  sinus  well  developed,  either  non-plicate 
or  with  a  single  median  plication;  lateral  slopes  of  the  valves  covered 
with  simple  plications,  and  the  whole  shell  marked  by  sublamellose,  con- 
centric lines  of  growth.  Pedicle  valve  with  a  moderately  high,  arched 
cardinal  area  having  an  open  delthyrium ;  internally  the  dental  plates  are 
well  developed  and  continue  to  the  inner  surface  of  the  valve  along  the 
lateral  margins  of  the  muscular  scar,  between  them  a  well  developed 
median  septum  is  present  which  extends  further  anteriorly  than  the 
dental  lamelke  and  may  reach  beyond  the  center  of  the  valve.  In  the 
brachial  valve  the  spiral  cones  are  directed  laterally  as  in  Spirifer,  the 
primary  lamelke  being  joined  by  a  simple  transverse  or  subacute  jugum. 
Shell  structure  strongly  punctate  throughout. 

Remarks. — Externally  the  members  of  this  genus  are  not  unlike  some 
small  species  of  the  genus  Spirifer,  the  essential  characters  by  which 
they  are  differentiated  from  that  genus  being  the  punctate  shell  structure 
and  the  very  strong  median  septum  in  the  pedicle  valve.  From  the  genus 
Delthyris,  Spiriferina  differs  essentially  only  in  the  punctate  shell  struc- 
ture, and  a  number  of  Mississippian  species  which  have  been  commonly 
referred  to  Spiriferina  heretofore,  but  in  which  no  punctate  shell  structure 
has  been  detected,  are  transferred  to  Delthyris  in  the  present  report. 

Spiriferina  subtexta  White 
Plate  XXXVI,  Figs.  35-40 

1S62.     Spiriferina  ?  subtexta  White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9, 

p.  25. 
1901.     Spiriferina  subtexta  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 

p.  199,  pi.  20,  figs.  5-6. 
1909.     Spiriferina  subtexta  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20.  p.  309, 

pi.   13,   figs.   16-19. 

Description. — Shell  small,  wider  than  long,  the  hinge-line  usually  a  little 
shorter  than  the  greatest  width  of  the  shell,  and  the  cardinal  extremities 
usually  ahruptly  and  narrowly  rounded.  The  dimensions  of  a  nearly 
perfect  pedicle  valve  are:    length  from  front  to  beak  10.5  mm.,  width 


292  MISSISSIPPIAN    BHACHIOPODA 

1")..")  mm.)  Length  of  hinge-line  13.5  mm.,  heighl  of  cardinal  area  -5.")  mm. 

Pedicle  valve  with  a  prominent  umbo,  the  surface  curving  rather  ab- 
ruptly anteriorly  to  the  front  margin  and  more  gently  laterally,  slightly 
or  not  at  all  compressed  towards  the  cardinal  extremities;  mesial  sinus 
sharply  defined,  originating  at  the  beak',  of  moderate  depth  and  width, 
SUbangular  at  the  bottom  ;  beak  rather  sharply  pointed,  incurved  ;  cardinal 
area  rather  high,  nearly  Hat  below  and  lying  in  nearly  a  right  angle  to  the 
plane  of  the  valve,  becoming  concave  above,  the  curvature  increasing 
towards  the  beak,  the  surface  abruptly  rounding  into  the  lateral  slopes 
of  the  valve  along  the  lateral  margins;  the  delthyrium  narrowly  triangu- 
lar, higher  than  wide;  each  lateral  slope  bearing  from  seven  to  nine 
simple,  rounded  or  subangular  plications  which  originate  near  the  car- 
dinal margin  and  grow  successively  smaller  towards  the  cardinal  ex- 
tremities, the  last    two  or  three  usually  being  very  faint. 

Brachial  valve  depressed  convex,  much  shallower  than  the  pedicle,  its 
greatest  convexity  near  the  middle,  compressed  towards  the  cardinal 
extremities;  mesial  fold  sharply  defined,  ronnded  on  top,  only  moderately 
elevated  above  the  general  surface  of  the  valve;  beak  small  and  incon- 
spicuous, scarcely  reaching  beyond  the  cardinal  margin;  cardinal  area 
very  narrow,  lying  in  nearly  the  plane  of  the  valve ;  lateral  slopes  bearing 
plications  similar  to  those  of  the  opposite  valve  and  alternate  with  them. 

Besides  the  plications,  each  valve  is  ornamented  by  fine,  regular,  con- 
centric, sublamellose,  imbricating  markings,  about  three  or  four  of  which 
occupy  the  space  of  one  millimeter.  When  the  shell  is  perefectly  pre- 
served the  surface  of  each  of  these  concentric  lamella1  is  regularly  fim- 
briate.   The  shell  structure  finely  and  closely  punctate. 

Remarks. — This  species  is  characterized  by  its  rather  high  area  and 
the  absence  of  a  median  plication  in  the  fold  and  sinus.  The  fimbriated 
character  of  the  fine  concentric  markings  of  the  shell  has  been  observed 
on  but  a  single  example,  but  it  was  doubtless  characteristic  of  all  during 
life.  The  punctate  structure  of  the  shell  is  also  usually  obscure  but  can 
usually  be  detected  upon  some  specimens  of  any  collection  by  close  ex- 
amination with  a  lens.  The  internal  characters  of  the  shell  have  not 
been  observed,  but  they  doubtless  conform  with  other  members  of  the 
genus. 

Horizon . — Kinderhook. 

Spiriferina  solidirostris  White 
Plate  XXXVI,  Figs.  25-34 

1860.     Spirifer  solidirostris  White,  Jour.  Boston  Soc.  Nat.  Hist.,  vol.  7. 

p.  232. 
1862.     Spiriferina  solidirostris  White,  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  9, 

p.  24. 
1865.     Spiriferina  solidirostris  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  120. 


SIMRIFERINA  293 

1899.     Spirifcrina  solidirostris  Girty,  Mon.  U.  S.  Cleol.  Survey,  vol.  32, 

p.  545,  pi.  71,  fig.  10a. 
1901.     Spirift  rina  solidirostris  Weller^  Trans.  St.  Louis  Acad.  Sci.,  vol.  11. 

p.  198,  pi.  20,  figs.  2-4. 
1903.     Spiriferina  solidirostris  Girty,  U.  S.  Geol.  Survey,  Prof.  Paper  No. 

Pi.  p.  294,  pi.  1.  figs.  3-4. 

Description.  —  Shell  below  medium  size,  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimen- 
sions of  a  pedicle  valve  are:  length  from  umbo  to  front  margin  12.5  mm., 
width  along  the  hinge-line  15  mm.,  convexity  6.7  mm.,  height  of  cardinal 
area  3  mm. 

Pedicle  valve  with  a  broad,  prominent  umbo,  the  surface  curving  rather 
abruptly  to  the  anterior  margin  and  sloping  to  the  cardinal  extremities 
with  a  slightly  sigmoidal  curve,  becoming  slightly  compressed  towards 
the  cardinal  extremities;  mesial  sinus  sharply  defined,  originating  at  the 
beak,  of  medium  width  and  depth,  marked  in  the  bottom  by  a  single, 
angular,  median  plication  which  originates  in  the  posterior  half  of  the 
valve ;  the  beak  pointed  and  strongly  incurved ;  the  cardinal  area  rather 
high,  nearly  flat  below  and  lying  almost  at  a  right  angle  to  the  plane 
of  the  valve,  becoming  concave  above  and  strongly  arched  towards  the 
beak,  the  apical  portion  sometimes  being  so  much  incurved  as  to  be 
directed  almost  towards  the  hinge-line ;  delthyrium  rather  large,  usually 
higher  than  wide,  often  retaining  the  pseudodeltidial  covering  towards 
the  apex;  lateral  slopes  marked  by  from  six  to  eight,  strong,  simple, 
rounded  plications  which  originate  along  the  cardinal  margin,  those 
bounding  the  sinus  are  the  strongest,  the  lateral  ones  becoming  pro- 
gressively smaller  towards  the  cardinal  extremities.  Internally  the  apical 
portion  of  the  valve  is  much  thickened  and  solidified,  and  the  rather 
strong  median  septum  extends  to  about  the  middle  of  the  valve,  the 
dental  plates  are  rather  short  and  thick  and  the  muscular  scars  are 
inconsjficuous. 

Brachial  valve  depressed  convex,  much  less  convex  than  the  opposite 
one,  the  greatest  convexity  usually  near  the  middle,  the  surface  some- 
what compressed  towards  the  cardinal  extremities;  the  mesial  fold  sharply 
defined,  originating  at  the  beak,  moderately  elevated  above  the  general 
surface  of  the  valve,  flattened  on  top  and  marked  by  a  single,  simple, 
mesial  furrow ;  the  beak  inconspicuous  and  scarcely  extending  beyond 
the  cardinal  margin ;  the  cardinal  area  very  narrow ;  lateral  slopes 
marked  by  plications  similar  to  those  of  the  opposite  valve  and  alternate 
with  them.    Internal  characters  not  observed. 

Besides  the  plications  each  valve  is  ornamented  by  regular,  concentric, 
sublamellose,  imbricating  markings,  about  two  or  three  of  wdiich  occupy 
the  space  of  one  millimeter.     The  shell  structure  is  punctate. 


294 


MISSISSIPPIAN    HK.U.'lIIOl'ODA 


Remarks.— This  species  of  Spiriferina  may  be  recognized  by  its  prom- 
inent umbo,  strongly  incurved  beak  of  the  pedicle  valve,  strongly  arched 
cardinal  area,  and  especially  by  the  median  plication  of  the  fold  and 
sinus.  Both  the  plications  and  concentric  markings  are  somewhat 
coarser  than  the  same  features  in  S.  siibh.rla.  In  no  case  have  the  con- 
cent rie  Lamella  given  evidence  of  being  fimbriate  upon  any  of  the  speci- 
mens observed,  as  is  the  ease  in  N.  sublcxta,  but  this  is  a  character  which 
is  easily  destroyed  and  the  shells  may  have  possessed  it  when  living.  The 
punctate  structure  of  the  shell  is  commonly  obscure  or  indeterminable 
upon  the  specimens,  hut  occasional  examples,  exfoliated  wholly  or  in  part, 
show   the  presence  of  the  perforations. 

Horizon-  -Kinderhook. 


Si'ikmi'i.kina   subelliptica    ( McChesney ) 

Plate  XXXVI,  Figs.  54-57 
1860.    Spirifa  r  subelliptica  McChesney,  Dese,  New  Pal.  Foss.,  p.  43. 

1894.  Spiriferina  subelliptica  Hall  and  Clarke,  Int.  to  Study  of  Brach., 

pt.  2,  pi.  2,  fig.  2. 

1895.  Spiriferina  subelliptica  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.   35,   figs.   21-22. 

Description.— Shell  of  medium  size  or  somewhat  larger,  transversely 
subelliptical  in  outline,  the  hinge-line  shorter  than  the  greatest  width  of 
the  shell,  the  cardinal  extremities  rounded,  the  greatest  width  posterior 
to  the  mid-length.  The  dimensions,  subject  to  error,  of  a  nearly  com- 
plete but  somewhat  crushed  specimen,  are :  length  of  pedicle  valve  19.5 
mm.,  length  of  brachial  valve  ±17  mm.,  greatest  width  28.5  mm.,  thick- 
ness estimated±12  mm.,  length  of  hinge-line  22.5  mm.,  height  of  cardinal 
area  3.5  mm.,  width  of  sinus  in  front  11.4  mm. 

Pedicle  valve  most  prominent  towards  the  umbo,  compressed  toward 
the  cardinal  extremities;  mesial  sinus  sharply  defined,  non-plicate,  origin- 
ating at  the  beak,  of  moderate  depth  and  rounded  in  the  bottom ;  beak 
rather  small,  pointed  and  incurved ;  cardinal  area  moderately  high,  con- 
cave with  the  curvature  increasing  towards  the  beak,  sometimes  the 
surface  of  the  area  rounds  into  the  lateral  slopes  of  the  valve  with  but  a 
slight  limiting  ridge,  but  more  often  the  lateral  margins  are  well  defined; 
delthyrium  rather  large,  as  high  or  higher  than  wide ;  each  lateral  slope 
marked  by  from  seven  to  eleven  simple,  rounded  plications  which 
originate  near  the  cardinal  margin  and  grow  successively  smaller  towards 
the  cardinal  extremities,  the  last  two  or  three  sometimes  being  very 
faint.  Internally  the  shell  is  much  thickened  in  the  apical  region,  a 
strong  median  septum  is  present  which  reaches  to  about  the  middle  of 
the  valve,  the  dental  plates  are  strong  and  short,  the  muscular  scars  are 
rather  small  and  only  moderately  distinct. 


SPIRIFERIXA  295 

Brachial  valve  less  convex  than  the  pedicle,  most  convex  posterior  to 
the  middle,  the  surface  curving  rather  abruptly  to  the  cardinal  margin 
and  gently  to  the  anterior  margin,  somewhat  compressed  towards  the 
cardinal  extremities;  mesial  fold  only  moderately  elevated  above  the 
general  surface  of  the  valve,  originating  at  the  beak,  sharply  defined, 
rounded  on  top;  beak  very  small,  scarcely  or  not  at  all  extended  beyond 
the  cardinal  margin;  cardinal  area  very  narrow;  the  lateral  slopes 
marked  by  plications  similar  to  those  of  the  opposite  valve  and  alternate 
with  them.  Internally  the  cardinal  process  is  small  and  inconspicuous, 
the  crural  plates  are  rather  strong  with  the  dental  sockets  excavated 
from  their  outer  surfaces;  the  muscular  scars  are  narrow  and  deeply 
excavated,  with  a  thickened,  marginal,  bordering  ridge  on  each  side 
which  continues  to  the  anterior  margin  of  the  valve. 

Surface  of  each  valve,  in  addition  to  the  plications,  ornamented  by 
fine  but  strong,  regular,  sublamellose,  imbricating,  concentric  markings 
which  are  finely  but  distinctly  fimbriate,  from  three  to  four  of  these 
markings  occupy  the  space  of  one  millimeter.  Shell  structure  minutely 
and  closely  punctate. 

h't  hi  arks. — This  species  has  been  rarely  recognized  since  its  original 
description  without  illustrations,  by  McChesney.  It  is  not  an  uncommon 
form  from  the  "Button  Mould  Knobs"  of  Kentucky,  but  its  horizon 
is  Kinderhook  rather  than  Kaskaskia,  as  stated  by  McChesney.  The 
species  is  the  largest  member  of  the  genus  in  the  faunas  here  considered, 
and  also  differs  from!  all  the  other  of  our  species,  except  $.  subtexta,  in  the 
finely  fimbriate  concentric  markings  of  the  shell. 

Horizon. — New  Providence  shale  of  Kinderhook,  Button  Mould  Knobs, 
Kentucky. 

Spiriferina  norwoodana  (Hall) 
Plate  XXXVI,  Pigs.  41-48 

1856.     Spirifcr  nonvoodana  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  7. 

1882.  Spiriferina  Nonvoodana  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1. 

p.  48.   pi.   6,   figs.   16-17. 

1883.  Spiriferina  norwoodana   Hall,    12th    Ann.    Eep.   Geol.   Surv.   Ind., 

p.  327,  pi.  29,  figs.  16-17. 
1906.     Spiriferina  norwoodana  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p. 
1311,  pi.  22.  figs.   16-17. 

Description. — Shell  small,  subsemielliptical  in  outline,  wider  than  long, 
the  hinge-line  a.  little  shorter  than  the  greatest  width  of  the  shell,  the 
greatest  width  posterior  to  the  mid-length  of  the  shell,  the  cardinal  ex- 
tremities rounded.  The  dimensions  of  a  nearly  perfect  specimen  are: 
length  of  pedicle  valve  3.1  mm.,  length  of  brachial  valve  3  mm.,  width 
4  mm.,  length  of  hinge-line  3.1  mm.,  thickness  2.8  mm.,  height  of  cardinal 
area  .8  mm.,  width  of  sinus  in  front  1.4  mm. 


296  J1ISSISSIPPIAN    BRACHIOPODA 

Pedicle  valve  strongly  convex,  mosl  prominenl  near  the  umbo,  the 
surface  curving  abruptly  to  the  cardinal  margin  ^  and  more  gently  to 
the  lateral  aud  anterior  margins,  sometimes  slightly  compressed  towards 
the  cardinal  extremities;  mesial  sinus  originating  at  the  beak,  of  moderate 
width  and  depth,  rounded  in  the  bottom;  beak  small,  pointed  or  mod- 
erately blunt,  incurved;  cardinal  area  small,  concave,  the  lateral  margins 
ill-defined,  rounding  into  the  Lateral  slopes  of  the  valve;  delthyrium  about 
as  wide  as  high ;  each  lateral  slope  marked  by  from  three  to  five,  simple, 
rounded  plications,  which  originate  at  or  near  the  cardinal  margin, 
those  bounding  the  mesial  sinus  are  much  the  stronger,  the  last  ones 
towards  the  cardinal  extremities  being  very  faint  or  almost  obsolete. 
Internally,  the  median  septum  is  reduced  to  a  slight  ridge  which  extends 
anteriorly  from  the  beak  for  about  one-third  the  length  of  the  valve,  the 
dental  plates  are  weakly  developed,  being  little  more  than  a  thickening 
of  the  valve  along  the  inner  margin  of  the  delthyrium. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  a  little  compressed  towards  the 
cardinal  extremities ;  mesial  fold  well  defined,  rounded,  but  little  elevated 
above  the  general  surface  of  the  valve,  sometimes  with  a  slight  mesial 
depression  towards  the  front ;  beaks  very  small  and  incurved ;  the  cardinal 
area  very  narrow;  plications  similar  to  those  of  the  opposite  valve  and 
alternate  with  them. 

Surface  of  both  valves,  when  well  preserved,  marked  by  minute  papilla?. 
Towards  the  front  of  the  shell  one  or  more  concentric  lines  of  growth 
are  frequently  present.     Shell  structure  minutely  punctate. 

Remarks. — The  specimen  whose  dimensions  have  been  given  above  is 
one  of  the  largest  members  of  the  species  which  has  come  under  obser- 
vation of  the  writer.  The  type  specimens  of  the  species,  however,  include 
somewhat  larger  individuals,  the  maximum  dimensions  recorded  by  Hall 
being  length  4.5  mm.  and  width  5.25  mm.  The  species  has  been  compared 
with  S.  spinosa  by  Whitfield,  who  seems  to  have  held  the  opinion  that  it 
might  be  only  a  diminutive  form  of  that  species.  It  resembles  S.  spinosa 
in  the  surface  ornamentation  of  the  shell,  but  besides  being  so  much  smaller, 
S.  norwoodana  is  more  rounded  at  the  cardinal  extremities,  has  a  much 
less  sharply  defined  cardinal  area,  and  more  broadly  rounded  plications, 
and  it  is  believed  that  the  two  forms  are  clearly  distinct  specifically. 

Horizon. — Salem  limestone. 

Spiriperina  salemensis  n.  sp. 

Plate  XXXVI,  Figs.  1-5 

Description. — Shell  below  medium  size,  broader  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimen- 
sions of  a  nearly  perfect  specimen  are :   length  of  pedicle  valve  16.3  mm., 


SPIRIFERINA  297 

length  of  brachial  valve  12.8  mm.,  width  along  hinge-line  22  mm.,  thick- 
ness 13.3  mm.,  height  of  cardinal  area  5.8  mm.,  width  of  sinus  in  front 
6  mm. 

Pedicle  valve  strongly  convex,  most  prominent  on  the  umbonal  region, 
the  surface  curving  steeply  from  the  umbo  to  the  anterior  margin  and 
more  gently  to  the  cardinal  extremities;  mesial  sinus  angular  or  sub- 
angular,  sharply  defined,  originating  at  the  beak,  of  moderate  depth  and 
width;  beak  small,  a  little  incurved;  cardinal  area  large  and  high,  nearly 
flat  below  and  lying  in  nearly  a  right  angle  to  the  plane  of  the  valve, 
concave  above  with  an  increasing  curvature  to  the  beak,  the  lateral 
margins  usually  sharply  defined;  the  delthyrium  large,  much  higher  than 
wide ;  each  lateral  slope  marked  by  about  five,  simple,  angular  or  sub- 
angular  plications  which  originate  along  the  cardinal  margin.  Internally 
a  strong  median  septum  reaches  anteriorly  from  the  beak  for  about  one- 
third  the  length  of  the  valve,  the  dental  plates  diverge  anteriorly  from 
the  beak  and  extend  about  one-half  as  far  as  the  median  septum ;  muscular 
scars  obscure. 

Brachial  valve  less  convex  than  the  pedicle,  highest  at  or  near  the  front 
of  the  mesial  fold,  the  surface  sloping  from  the  front  margin  of  the  fold 
to  the  beak  in  an  increasingly  convex  curve,  becoming  a  little  compressed 
towards  the  cardinal  extremities ;  mesial  fold  angular,  sharply  defined, 
much  elevated  in  front;  cardinal  area  very  narrow,  lying  in  nearly  a 
right  angle  to  that  of  the  opposite  valve ;  the  beak  small,  incurved ;  each 
lateral  slope  marked  by  angular  plications  similar  to  those  of  the  opposite 
valve  and  alternate  with  them. 

Surface  of  both  valves  marked  by  numerous,  concentric  lines  of  growth, 
irregular  in  strength  and  crowded  at  intervals  towards  the  front  to  form 
stronger  growth  lines.    Shell  structure  minutely  punctate. 

Remarks. — This  is  the  more  common  species  of  Spiriferina  in  the  fauna 
of  the  Salem  limestone,  and  has  sometimes  been  identified  as  8.  spinosa. 
It  differs  from  that  species  in  its  much  more  elevated  cardinal  area,  in 
its  more  angular  plications,  more  elevated  mesial  fold  in  front,  and  in  the 
very  different  style  of  surface  markings.  •  It  is  very  different  from  the 
diminutive  S.  norwoodana  of  the  same  fauna,  and  cannot  be  considered  as 
a  larger  form  of  the  same  species. 

Horizon.— Salem  limestone. 

Spiriferina  transversa  (McChesney) 
Plate  XXXV,  Figs.  41-49 

I860.     Spirifer  transversa  McChesney,  Dese.  New  Pal.  Foss.,  p.  42. 
1865.     Spirifer  transversa  McChesney,  111.  New  Spec.  Foss.,  pi.  6,  fig's.  3a-c. 
3868.     Spirifer  transversa  McChesney,  Trans.  Chicago  Acad.  Sci.,  vol.  1, 

p.  34,  pi.  6,  figs.  3a-c. 
1874.     Spiriferina  transversa  Derbv,  Bull.  Cornell  Univ.  (Science),  vol.  1, 

No.  2,  p.  21,  pi.  2,  figs.  4,  6,  13;  pi.  3,  figs.  12,  14,  17;  pi.  5,  fig.  4. 


298  MISSISSIPPIAN    BRACHIOPODA 

1883.     Spin/,  ni  transversa  Hall,  Rep.  N.  V.  Slate  Geol.  for  1882,  pi.  (35) 

60,  figs.  19-25. 
L894.     Spiriferina  tra/nsversa   Hal]  and  Clarke,  Int.  to  Study  of  Brach., 

pt.  2,  pi.  31,  figs.  1-3. 
1895.     Spiriferina  transversa   Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  35,  fin's,  li),  20,  23-25. 

Description.  Shell  below  medium  size,  broadly  subtriangular  in  outline, 
usually  more  than  twice  as  wide  as  long  and  the  thickness  about  equal  to 
the  Length,  the  cardinal  extremities  acutely  pointed.  The  dimensions  of  a 
very  perfect  specimen  are:  length  of  pedicle  valve  10  mm.,  length  of 
brachial  valve  9  mm.,  width  along  hinge-line  25.1  mm.,  thickness  9.6  nun., 
height  of  cardinal  area  3  mm.,  width  of  mesial  sinus  in  front  4.2  mm. 

Pedicle  valve  strongly  convex,  most  prominent  in  the  umbonal  region, 
the  surface  sh.|>ing  from  the  umbo  to  the  cardinal  extremities  in  a  nearly 
straighl  or  slightly  concave  line  and  curving  strongly  to  the  anterior 
margin;  the  mesial  sinus  originating  at  the  beak,  of  moderate  width  and 
depth,  sharply  defined,  marked  by  a  single  median  plication  which  orig- 
inates in  the  umbonal  region  ;  the  beak  rather  small,  pointed  and  incurved; 
cardinal  area  large,  concave,  with  the  curvature  increasing  towards  the 
beak,  its  lateral  margins  sharply  defined,  its  lower,  flatter  portion  standing 
at  nearly  a  right  angle  to  the  plane  of  the  valve;  delthyrium  large,  nearly 
as  wide  as  high  ;  each  lateral  slope  marked  by  from  ten  to  twelve  simple, 
rounded  plications  which  originate  along  the  cardinal  margin,  those 
bounding  the  mesial  sinus  are  the  largest  and  they  grow  regularly 
smaller  towards  the  cardinal  extremities,  the  last  ones  being  very  faint 
or  nearly  obsolete.  Internally  a  strong  median  septum  extends  from 
the  beak  to  about  the  middle  of  the  valve,  the  hinge-teeth  are  strengthened 
by  dental  lamella?  which  continue  to  the  floor  of  the  valve  and  diverge 
anteriorly,  extending  about  one-half  or  a  little  less  than  one-half  as  far 
as  the  median  septum. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  curving  abruptly  from  the  point  of 
greatest  convexity  to  the  cardinal  margin  and  more  gently  to  the  anterior 
margin,  towards  the  cardinal  extremities  the  surface  is  somewhat  com- 
pressed ;  mesial  fold  sharply  defined,  originating  at  the  beak,  flattened  on 
top  and  marked  by  a  median  furrow  which  originates  back  of  the  middle 
of  the  valve ;  the  beak  small,  strongly  incurved ;  the  cardinal  area  very 
narrow,  making  an  angle  of  about  90  degrees  to  that  of  the  opposite 
valve ;  each  lateral  slope  marked  by  plications  similar  to  those  of  the 
opposite  valve  and  alternate  with  them.  Internally,  the  cardinal  process 
is  of  moderate  size  and  is  flanked  by  the  rather  strong  crural  plates  in 
the  outer  faces  of  which  the  dental  sockets  are  excavated ;  the  muscular 
scars  are  weakly  developed  and  are  divided  longitudinally  by  a  faint 
median  ridge. 


SPIRIFERINA  299 

In  addition  to  the  plications  the  surface  of  each  valve  is  marked  by 
fine,  regular,  imbricating,  sublamellose  lines,  about  four  of  which  occupy 
the  space  of  one  millimeter.  The  shell  substance  is  finely  punctate,  the 
perforations  having  a  tendency  to  be  arranged  in  concentric  lines,  al- 
though this  arrangement  is  not  perfectly  carried  out. 

Remarks. — This  species  may  be  easily  recognized  by  the  great  width  of 
the  shell  and  by  the  mesial  plication  in  the  fold  and  sinus.  In  this  latter 
character  it  resembles  S.  solidirostris  from  a  much  lower  horizon  in  the 
Mississippian,  and  occasionally  an  individual  with  less  extended  hinge- 
line  than  common,  rather  closely  resembles  the  earlier  species,  but  or- 
dinarily S.  transversa  has  somewhat  finer  plications  than  S.  solidirostris, 
and  a  narrower  umbonal  region.  The  chief  variation  shown  by  different 
individuals  of  the  species  is  in  the  proportional  width  of  the  shell.  The 
specimen  whose  dimensions  have  been  given  is  an  entirely  normal  indi- 
vidual, hut  occasionally  examples  occur  whose  length  is  fully  two-thirds 
the  width,  but  they  possess  the  characters  of  the  species  in  all  other 
respects  and  are  united  with  the  normal  form  by  intermediate  variations. 

Horizon.  —  Chester  group. 

Spiriferina  spinosa   (Norwood  and  Pratten) 

Plate  XXXV,  Figs.  50-58 

1855.     Spirift  r  spinosus  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci.,  Phil., 

(2),  vol.  3,  p.  71,  pi.  9,  figs.  la-d. 
1858.     Spirif  cr  spinosus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  706,  pi.  27,  figs. 

5a-c. 
j 883.     Spiriferina  spinosa  Hall,  Rep.  N.  Y.  State  (ieol.  for  1882,  pi.  (35  ^ 

60,  figs.  26-2! t. 
1894.     Spirif  erina  spinosa  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pi.  31,  figs.  4-7. 
1894.     Spiriferina  spinosa  Keyes,  Mo.  Geol.  Surv..  vol.  5,  p.  85. 
]l  895.     Spiriferina  spinosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  35. 

figs.  26-29. 

Description.— Shell  below  medium  size,  broader  than  long,  the  greatest 
width  along  the  hinge-line  or  a  little  anterior  to  it,  the  cardinal  extremi- 
ties angular  or  a  little  rounded.  The  dimensions  of  two  perfect  speci- 
mens are :  length  of  pedicle  valve  14.2  mm.  and  12.5  mm.,  length  of 
brachial  valve  11.5  mm.  and  10.3  mm.,  width  18.7  mm.  and  20.4  mm.,  thick- 
ness 12.5  mm.  and  9.8  mm.,  height  of  cardinal  area  2.6  mm.  and  2.4  mm., 
width  of  mesial  sinus  in  front  6.1  mm.  and  5.3  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbo  prominent, 
the  surface  curving  abruptly  to  the  cardinal  margin  and  more  gently  to 
the  anterior  margin,  often  a  little  compressed  towards  the  cardinal  ex- 
tremities; the  mesial  sinus  sharply  defined,  originating  at  the  beak,  of 
moderate  width  and  rather  deep,    subangular    in    the    bottom;  the  beak 


;;oo 


MISSISSIPPIAN    BKACIIIOPODA 


rather  small,  pointed  and  incurved;  cardinal  area  of  moderate  height, 
concave  with  the  curvature  increasing  towards  the  beak,  the  lower  and 
Hatter  portion  lying  at  oearly  a  right  angle  to  the  plane  of  the  valve,  the 
lateral  margins  well  denned  hut  rounding  rather  abruptly  to  the  lateral 
slopes  of  the  valve:  dell hyrium  ahout  as  wide  as  high;  each  lateral  slope 
marked  by  five  or  six  rounded  or  subangular,  simple  plications,  which 
originate  along  the  cardinal  margin,  those  bounding  the  mesial  sinus  are 
the  Strongest,  the  others  becoming  successively  smaller  to  the  cardinal  ex- 
tremities. Internally  a  slrong  median  septum  reaches  from  the  beak  to 
more  than  one-third  the  length  of  the  valve,  the  hinge-teeth  are  supported 
by  dental  plates  which  diverge  anteriorly  and  extend  about  one-third  as 
far  as  the  median  septum. 

Brachial  valve  nearly  or  quite  as  convex  as  the  pedicle,  the  greatest 
depth  near  the  middle  or  towards  the  front  of  the  mesial  fold;  the  surface 
convex  on  each  side  of  the  fold,  usually  becoming  a  little  compressed 
towards  the  cardinal  extremities;  mesial  fold  rounded  or  subangular, 
sharply  defined,  moderately  or  rather  highly  elevated  in  front;  the  beak 
small  and  incurved;  the  cardinal  area  very  narrow,  lying  in  nearly  the 
plane  of  the  valve;  the  plications  on  the  lateral  slopes  are  similar  to  those 
of  the  opposite  valve  and  alternate  with  them. 

Surface  of  both  valves,  when  well  preserved,  marked  by  crowded  tuber- 
cles which  are  the  bases  of  spinules  which  are  scattered  in  position  or 
sometimes  are  arranged  in  rather  irregular  radiating  rows.  One  or  more 
rather  strong  lines  of  growTth  are  sometimes  present  towards  the  anterior 
margin  of  the  valves.     Shell  substance  punctate. 

h'<  marks. — This  species  occurs  commonly  in  some  of  the  Chester  faunas 
and  can  be  easily  recognized  by  the  character  of  the  surface  markings. 
It  may  be  easily  distinguished  from  S.  transversa,  with  which  it  is  some- 
times associated,  by  its  proportionally  narrower  and  longer  shell,  by  the 
absence  of  a  median  plication  in  the  fold  and  sinus,  and  by  its  surface 
markings. 

Horizon  —  Chester  group 

Genus  DELTHYEIS  Dalman 

Description. — Shell  small  or  of  medium  size,  spiriferoid  in  external  form, 
the  mesial  fold  and  sinus  non-plicate  or  with  a  single  median  plication, 
the  lateral  slopes  of  the  valves  with  simple,  rather  strong  plications,  both 
valves  marked  by  concentric,  lamellose  lines  of  growth  of  greater  or  less 
strength.  Pedicle  valve  with  an  arched  cardinal  area  of  moderate  height, 
and  an  open  delthyrium ;  internally  the  dental  lamella?  are  well-develpoed 
and  between  them  is  a  well-defined  median  septum.  The  brachial  valve  is 
similar  to  Spirifer  internally,  with  a  brachidium  as  in  that  genus. 

Remarks.  —  The  genus  Delthyris  commonly  has  not  been  recognized  above 
the  Devonian,  but  there  is  a  group  of  small  Spiriferina-like  shells  in  our 


DELTHYRIS  301 

early  Mississippian  faunas  which  are  apparently  wholly  devoid  of  punctate 
shell  structure  and  must  consequently  be  excluded  from  Spiriferina,  and 
the  genus  Ddtlryris  is  apparently  the  only  place  where  they  can  be  prop- 
erly located.  The  only  essential  difference  between  Delthyris  and  Spiri- 
ferina, as  interpreted  by  Sehuchert,1  and  followed  by  the  author, 
is  in  the  absence  of  punctation  in  Delthyris.  Both  genera  are  characterized 
by  the  well  developed  median  septum  in  the  pedicle  valve,  by  the  simple 
plications  of  the  shell,  by  the  strong,  concentric,  lamellose  lines  of  growth, 
and  by  the  essentially  spiriferoid  external  form.  It  is  believed  that  the 
shells  here  placed  in  the  genus  are  actually  devoid  of  punctations  and 
that  their  absence  is  not  due  to  the  condition  of  preservation  since  the 
structure  can  always  be  detected  to  some  extent,  at  least,  in  all  the  un- 
doubted Spiriferinas,  whatever  their  condition  of  preservation,  but  in 
these  shells  it  has  never  been  detected. 

Delthyris  clarksvillensis    (AVinchell) 
Plate  XXXVI,  Figs.  6-7 

1865.     Spiriferina  Clarksvillensis  Winchell,   Proc.   Acad.  Nat.   Sci.  Phil., 

p.  119. 
1894.     Spiriferina  clarkesvillensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  85. 
1908.     Spiriferina  clarksvillensis  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol. 

8,  2nd  her.,  p.  83,  pi.  18,  figs.  10-12. 

Description. — Shell  below  medium  size,  wider  than  long,  hinge-line  as 
long  as,  or  a  little  shorter  than,  the  greatest  width  of  the  shell,  the  cardinal 
extremities  angular  or  a  little  rounded.  The  dimensions  of  a  nearly  com- 
plete but  somewhat  distorted  specimen  are :  length  of  pedicle  valve  11 
mm.,  length  of  brachial  valve  9.1  mm.,  width  16.8  mm.,  thickness  ±8  mm., 
width  of  sinus  in  front  5.4  mm.,  height  of  cardinal  area  3.9  mm. 

Pedicle  valve  moderately  convex,  most  prominent  on  the  umbo,  but 
little  or  not  at  all  compressed  towards  the  cardinal  extremities,  the  sur- 
face curving  rather  abruptly  to  the  cardinal  margin  on  each  side  of  the 
beak,  more  gently  to  the  anterior  margin  and  most  gently  to  the  lateral 
margins ;  mesial  sinus  rather  wide,  of  moderate  depth,  non-plicate,  and 
rounded  in  the  bottom ;  beak  only  moderately  incurved ;  cardinal  area  of 
moderate  height,  nearly  flat  below,  becoming  concave  towards  the  beak, 
the  lateral  margins  sharply  defined  or  rounding  slightly  into  the  surface 
of  the  lateral  slopes;  the  delthyrium  of  moderate  size,  higher  than  wide; 
each  lateral  slope  marked  by  from  four  to  seven,  rather  broad,  rounded, 
plications  which  originate  along  the  cardinal  margin.  Internally  a  me- 
dian septum  is  present  which  reaches  between  one-third  and  one-half  the 
length  of  the  shell  from  the  beak,  the  remaining  internal  characters  not 
observed. 

l  Synop.  Am.  Foss.  Brach.,  Bull.  87,  U.  S.  Geol.  Survey,  p.  206.    (1897.) 


:!(I*J  MISSISSIPPIAN   BRACHIOPODA 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  compressed  towards  Ihe  cardinal  extremities;  the  mesial 
fold  rounded,  but  little  elevated  above  the  general  surface  of  the  valve; 
cardinal  area  very  narrow,  lying  in  nearly  the  plane  of  the  valve;  plica- 
tions similar  to  those  of  the  opposite  valve  and  alternate  with  them.  In- 
ternal characters  not  observed. 

Besides  the  plications  the  surface  of  each  valve  is  ornamented  by  con- 
spicuous, somewhat  irregular,  lamellose,  imbricating,  concentric  markings, 
about  two  or  three  occupying  the  space  of  one  millimeter. 

"Remarks.-  In  none  of  the  .specimens  of  this  species,  which  have  been 
examined  by  the  writer,  has  the  punctate  shell  structure  of  the  genus  Spiri- 
ferina been  observed.  In  the  original  description  of  the  species,  however, 
it  is  stated  "internal  surface  of  the  valve  marked  with  numerous  indented 
punctations,"  and  this  would  seem  to  indicate  that  the  species  possesses 
this  characteristic  structure  of  the  genus  Spiriferina.  Not  infrequently 
in  undoubted  species  of  Spiriferina,  this  structure  is  obscure  and  cannot  be 
detected  upon  many  examples,  but  an  examination  of  a  sufficient  number  of 
specimens  usually  leads  to  its  recognition.  This  species  differs  from  most  of 
the  other  members  of  the  genus  here  described,  also  from  members  of  the 
genus  Spiriferina,  in  its  stronger  and  coarser  concentric  lamella-.  The 
number  of  plications  is  a  somewhat  variable  character,  but  they  are  al- 
ways coarser  and  less  numerous  than  usual  in  the  genus.  The  species 
which  most  closely  resembles  this  one  is  D.  missouriensis,  and  the  differences 
between  the  two  forms  will  be  considered  under  the  discussion  of  that 
species. 

Horizon. — Louisiana  limestone. 

Delthyris  missouriensis  Weller 
Plate  XXXVI.  Figs.  9-14 

1906.     Delthyris  missGuriensis  Weller,  Trans.  St.  Louis  Acad.  Sei..  vol.  16. 
p.  445,  pi.  6,  figs.  23-26. 

Description. — Shell  smjall.  wider  than  long,  the  greatest  width  usually  a 
little  in  front  of  the  hinge-line,  and  the  cardinal  extremities  narrowly 
rounded.  The  dimensions  of  a  pedicle  valve  are :  length  from  umbo  to 
front  margin  10  mm.,  width  12.5  mm.,  length  of  hinge-line  11  mm.,  convex- 
ity 4.5  mm.,  height  of  cardinal  area  2.2  mm.  The  dimensions  of  a  large 
brachial  valve  are:  length  9  mm.,  width  13.4  mm.,  convexity  3  mm. 

Pedicle  valve  rather  strongly  convex,  the  convexity  extending  out  to 
the  cardinal  extremities,  the  umbo  prominent,  the  surface  curving  rather 
abruptly  to  the  anterior  margin  and  sloping  in  nearly  straight  lines  to 
the  cardinal  extremities;  mesial  sinus  originating  at  the  beak,  of  moderate 
width,  rather  shallow,  and  rounded  or  somewhat  flattened  in  the  bottom : 
the  beak  rather  obtuse,    a    little    incurved;    cardinal    area  of  moderate 


DELTHYRIS  303 

height,  only  slightly  concave,  the  lateral  margins  angular  and  well- 
defined  ;  the  delthyrium  narrowly  triangular,  higher  than  wide ;  each  lat- 
eral slope  bearing  three  or  four  simple,  rounded  plications  which  origin- 
ate near  the  cardinal  margin.  Internally  the  valve  bears  a  distinct  median 
septum. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
the  middle,  the  surface  a  little  compressed  towards  the  cardinal  extremi- 
ties; mesial  fold  rounded,  but  little  elevated  above  the  general  surface  of 
the  valve ;  the  plications  similar  to  those  of  the  opposite  valve  and  alter- 
nate with  them. 

Besides  the  plications  the  surface  of  each  valve  is  ornamented  by  strong, 
crowded,  sublamellose,  concentric  markings,  three  or  four  of  which  occupy 
the  space  of  one  millimeter. 

Remarks. — This  species  most  closely  resembles  D.  clarksviUensis,  agreeing 
with  that  species  in  its  rather  shallow,  rounded  sinus  and  low  fold,  in 
the  rather  coarse  rounded  plications,  and  in  the  stronger  and  coarser 
concentric  lamellose  markings  of  the  shell  than  is  usual  in  other  species. 
D.  missouri&nsis  differs  from  D.  clarksviUensis  in  its  somewhat  narrower 
shell  and  more  convex  pedicle  valve,  and  in  the  smaller  number  of  plica- 
tions. The  specimens  whose  dimensions  have  been  given  are  among  the 
largest  ones  observed,  a  great  number  of  individuals  having  a  width  of 
less  than  5  mm. 

Formation.— Glen  Park  limestone  and  Hamburg  oolite  of  the  Kinder- 
hook. 

Delthyris  suborbicularis  Weller 

Plate  XXXVI,  Fig.  8 

1906.     Delthyris  suborbicularis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  16 
p.  446,  pi.  6,  figs.  27-28. 

Description. — Shell  small,  broader  than  long,  the  hinge-line  shorter  than 
the  greatest  width,  the  cardinal  extremities  rounded.  The  dimensions 
of  a  pedicle  valve  are :  length  10.5  mm.,  width  11.7  mm.,  length  of  hinge- 
line  8.7  mm.,  convexity  3  mm.,  height  of  cardinal  area  2.3  mm. 

Pedicle  valve  moderately  convex,  the  convexity  extending  out  to  the 
cardinal  extremities,  the  surface  sloping  with  a  gently  convex  curvature 
from  the  umbo  to  the  anterior  and  lateral  margins;  mesial  sinus  originat- 
ing at  the  beak,  rather  broad  and  shallow,  rounded  in  the  bottom ;  the 
beak  obtuse,  scarcely  incurved ;  cardinal  area  slightly  concave,  sloping 
posteriorly  from  the  hinge-line  and  lying  at  an  angle  of  about  130  degrees 
to  the  plane  of  the  valve,  the  lateral  margins  not  sharply  defined,  the 
surface  rounding  into  that  of  the  lateral  slopes  of  the  valve ;  delthyrium 
higher  than  wide ;  each  lateral  slope  bearing  five  or  six  simple,  low, 
rounded  plications  which  originate   near   the    cardinal   margin  and  grow 


•MU 


MISSISSIPPIAN    BKACIIIOI'ODA 


successively  smaller  towards  the  cardinal  extremities.  Enternally  a 
strong  median  septum  reaches  from  the  beak  to  ;i  point  between  one- 
third  and  one-half  the  length  of  the  valve,  the  dental  plates  diverge 
anteriorly  from  the  beak  and  reach  anteriorly  less  than  one-half  the 
length  of  the  median  septum. 

Brachial   valve  qo1   known. 

Surface  of  the  shell  ornamented  by  rather  strong,  regular,  sublamellose, 
concentric  markings,  aboul  three  <>r  tour  of  which  occupy  the  space  of 
one  millimeter. 

Remarks.  The  species  differs  from  its  associate,  S.  missouriensis,  in  the 
less  strongly  convex  pedicle  valve,  in  the  nearly  flat  cardinal  area  with 
its  posteriorly  sloping  position,  in  the  more  obtuse  beak  of  the  pedicle 
valve,  and   in  the  greater  number  of  plications. 

Horizon.— Glen   Park  limestone  of  the  Kinderhook. 


Delthybis  novamexicana   (Miller) 
Plate  XXXVI.  Figs.  15-24 

J.881.     Spirifera  novamexicana  Miller,  Jour.  ('inn.  Soc.  Nat.  Hist.,  vol.  4, 

p.  314,  pi.  7,  figs  10-10b. 
1909.     Spiriferina  magnicostatus  Weller,  Bull.  Geol.  Soc.    Am.,    vol.  20, 

p.  307,  pi.  13,  figs.  12-15. 

Description. — Shell  small,  much  broader  than  long,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  often  produced  into  slender, 
mucronate  extensions.  The  dimensions  of  a  somewhat  imperfect  and 
distorted  specimen,  more  than  usually  extended  along  the  hinge-line, 
are:  length  of  pedicle  valve  -(-7  mm.,  length  of  brachial  valve  6  mm., 
width  along  hinge-line  24  mm.,  thickness  ±6  mm. 

Pedicle  valve  most  prominent  in  the  uinbonal  region,  becoming  com- 
pressed towards  the  cardinal  extremities ;  the  mesial  sinus  of  moderate 
depth,  rounded  in  the  bottom,  bounded  laterally  by  a  pair  of  strong, 
rounded  ribs  which  originate  at  the  beak  and  which  are  prominently  ele- 
vated above  the  plications  on  either  side;  the  beak  rather  small,  pointed 
and  incurved;  the  cardinal  area  low,  concave,  with  its  lateral  margins 
sharply  defined;  the  delthyrium  about  as  wide  as  high;  lateral  slopes 
convex  from  the  cardinal  to  the  anterior  margins,  the  slope  from  the 
umbo  to  the  cardinal  extremities  concave,  each  one  marked  by  three  or 
sometimes  four  clearly  defined,  rounded  plications,  beyond  those  which 
bound  the  mesial  sinus,  they  originate  along  the  cardinal  margin,  and 
decrease  gradually  in  size  towards  the  cardinal  extremities,  and  on 
shells  greatly  extended  along  the  hinge-line  one  or  more  additional, 
extremely  faint  plications  may  sometimes  be  detected ;  the  largest  of  the 
lateral  plications  are  distinctly  smaller  than  those  which  bound  the 
mesial  sinus.     Internally,  the  umhonal  portion  of  the  valve  is  solidified, 


DELTIIVRlS  305 

at  least  in  mature  shells,  the  muscular  scar  is  strongly  denned  and  is 
divided  longitudinally  by  an  angular  ridge  which  becomes  more  septum- 
like towards  the  beak,  and  which  in  young  examples  with  less  completely 
solidified  beaks,  perhaps  became  a  distinct  median  septum;  the  dental 
plates  are  short,  scarcely  more  than  ridge-like  thickenings  of  the  shell 
along  the  inner  borders  of  the  delthyrium. 

Brachial  valve  less  convex  than  the  pedicle,  greatest  convexity  near 
or  posterior  to  the  middle,  compressed  towards  the  cardinal  extremities ; 
mesial  fold  but  little  elevated  above  the  general  surface  of  the  valve, 
rounded  or  flattened  on  top,  sometimes  with  a  faint  mesial  line  which  is 
scarcely  a  depressed  furrow ;  the  plications  of  the  lateral  slopes  similar 
to  those  of  the  opposite  valve  and  alternate  with  them,  the  furrows 
bounding  the  mesial  fold  somewhat  deeper  and  broader  than  those  be- 
tween the  other  plications. 

In  addition  to  the  plications  the  surface  of  each  valve  is  ornamented 
by  strong,  regular,  sublamellose,  imbricating,  concentric  markings,  four 
or  five  of  which  occupy  the  space  of  one  millimeter,  and  which  are 
fimbriate  along  their  margins. 

Remarks. — This  species  is  characterized  by  the  great  breadth  of  the 
shell,  its  mucronate  cardinal  extremities,  and  the  strong  plications 
bounding  the  sinus  of  the  pedicle  valve.  The  punctate  structure 
which  these  shells  should  exhibit  if  they  belong  to  the  genus  Spirifi  rina 
has  not  been  observed,  and  consequently  the  species  is  referred  to  the 
genus  DeWiyris.  Perhaps  a  more  important  deviation  from  the  typical 
structure  of  Spiriferina  is  the  absence  of  a  true  median  septum  in  the 
pedicle  valve.  There  is  along  the  median  line  of  the  muscular  scar  a 
distinct,  broadly  angular  median  ridge,  but  it  can  scarcely  be  interpreted 
as  a  median  septum  in  the  mature  condition  of  the  shell  at  least.  It 
may  have  been  such  in  the  younger  stages  of  growth,  before  the  apical 
portion  of  the  valve  became  so  solidified  as  it  is  in  the  mature  specimens, 
but  the  interior  of  such  young  examples  has  not  been  observed. 

Horizon. — Fern  Glen  formation. 

Delthyris  similis  n.  sp. 

Plate  XXXVI,  Pigs.  49-53 

Description. — Shell  small,  much  wider  than  long,  the  greatest  width 
along  the  hinge-lint',  the  cardinal  extremities  subrectangular,  the  lateral 
and  anterior  margins  regularly  rounded  or  the  anterior  margin  somewhat 
truncated  in  the  middle.  The  dimensions  of  a  nearly  complete  internal 
cast  in  chert  are :  length  of  pedicle  valve  14  mm.,  length  of  brachial 
valve  10  mm.,  width  19  mm.,  thickness  12  mm.,  height  of  cardinal  area  4 
mm.,  width  of  mesial  sinus  in  front  6.6  mm. 


306 


MISSISSIPPIAN   HKACIIIOPODA 


Pedicle  valve  strongly  convex,  the  surface  sloping  with  a  gently  convex 
curvature  from  the  umbonal  region  to  the  cardinal  extremities,  and 
curving  more  abruptly  to  the  anterior  margin;  mesial  sinus  originating  at 
the  beak,  sharply  defined,  rounded  in  the  bottom,  becoming  rather  deep 
anteriorly  and  produced  in  a  rounded,  lingual  extension  in  front,  of 
greater  or  less  length  ;  beak  moderately  incurved,  remote  from  that  of  the 
opposite  valve;  cardinal  area  high,  concave,  with  the  concavity  increasing 
towards  the  beak,  the  lateral  margins  sharply  defined,  sloping  from  the 
beak  to  the  cardinal  extremities  with  an  increasingly  convex  curvature 
distally,  the  delthyrium  higher  than  wide.  Surface  of  valve  marked  by 
strong,  simple,  rounded  or  subangular  plications  which  originate  at  the 
beak  or  along  the  cardinal  margin,  the  mesial  sinus  is  marked  by  a  single 
faint  plication  along  its  median  line  which  may  be  entirely  obsolete  in 
the  internal  casts;  each  lateral  slope  marked  by  from  six  to  eight,  plica- 
tions which  become  successively  fainter  towards  the  cardinal  extremities; 
concentric  lines  of  growth  mark  the  valve  which  not  infrequently  become 
rather  strong  towards  the  margin.  Internally  the  dental  lamellae  are  well 
developed  and  sometimes  extend  anteriorly  for  one-fourth  the  length  of' 
the  valve  from  the  beak,  following  the  lines  of  the  first  intercostal  furrows 
each  side  of  the  sinus ;  between  the  dental  lamella;  is  a  strong  median 
septum  which  extends  farther  anteriorly  than  the  dental  lamella?,  some- 
times nearly  to  the  middle  of  the  valve. 

Brachial  valve  somewhat  less  convex  than  the  pedicle,  its  greatest 
convexity  near  or  in  front  of  the  middle,  the  surface  curving  more 
abruptly  to  the  cardinal  margin  towards  the  beak,  usually  a  little  de- 
pressed towards  the  cardinal  extremities;  the  mesial  fold  well  defined 
by  furrows  which  are  wider  and  deeper  than  those  between  the  plications, 
becoming  rather  highly  elevated  towards  the  front,  flattened  on  top  with  a 
median  furrow  which  is  more  conspicuous  than  the  median  rib  of  the 
sinus  of  the  opposite  valve ;  beak  small,  moderately  incurved.  Surface 
marked  by  plications  similar  in  number  and  form  to  those  of  the  opposite 
valve,  and  by  similar  concentric  lines  of  growth.  Internally  a  slight 
median  ridge  extends  anteriorly  from  the  beak  to  near  the  middle  of  the 
valve. 

Remarks. — In  general  form  and  size  this  species  resembles  Cyrtina 
neogenes,  and  the  two  shells  have  sometimes  been  confused.  In  the  con- 
dition of  internal  casts  in  chert,  the  only  condition  in  which  either  of 
these  species  have  been  certainly  recognized,  D.  similis  can  always  be  rec- 
ognized by  the  presence  of  three  distinct  slits  diverging  anteriorly  from 
the  beak  of  the  pedicle  valve,  representing  the  dental  lamella?  and  the 
median  septum,  while  in  C.  neogenes  a  single  median  slit  is  present.  The 
plications  of  D.  similis,  also,  are  usually  somewhat  more  subangular  than 
those  of  C.  neogenes,  and  by  this  character  the  brachial  valves  of  the  two 


SPIRIFKR  307 

species  may  be  differentiated.  In  none  of  the  easts  of  this  species  which 
have  been  examined,  lias  any  punctate  structure  of  the  shell  been  ob- 
served, but  this  shell  structure  is  almost  without  exception  well  shown 
upon  the  casts  of  C.  ncoyatcs  by  the  fine  papilla1  which  are  the  casts  of  the 
original  perforations  of  the  shell.  The  fine  surface  markings  have  not 
been  observed  in  this  species  because  of  the  lack  of  proper  external  im- 
pressions of  the  shell,  such  as  have  been  seen  of  C.  neogt  nes.  The  species 
was  clearly  well  marked  by  concentric  growth  lines,  but  it  is  not  known 
that  they  were  such  strongly  lamellose  and  regular  markings  as  are 
characteristic  of  many  species  of  Delthyris.  It  is  believed  that  this  was 
their  character,  a  character  which,  in  the  absence  of  a  punctate  shell 
structure,  would  throw  the  species  into  the  genus  Delthyris  rather  than 
Spiriferina. 

Horizon. — Residual  chert,  probably  of  Keokuk  age. 

Genus  SPIRIFER  Sowerby 
Description. —  Shells  varying  in  size  from  small  to  very  large,  usually 
wider  than  long,  rarely  longer  than  wide,  the  hinge-line  straight, 
shorter  than  the  greatest  width  of  the  shell  and  the  cardinal  extremities 
rounded;  or  more  frequently  the  greatest  width  of  the  shell  along  the 
hinge-line  and  the  cardinal  extremities  angular  and  more  or  less  extended, 
sometimes  conspicuously  acuminate.  Mesial  sinus  in  the  pedicle  valve 
and  fold  in  the  brachial  valve  usually  well  developed,  more  rarely  with- 
out fold  or  sinus.  Surface  of  both  valves  marked  by  radiating  plications 
which  may  be  simple  without  division  from  the  point  of  origin  at 
the  cardinal  margin  to  the  anterior  margin,  or  may  divide  in  various 
manners ;  the  plications  may  be  present  upon  the  lateral  slopes  only  or 
upon  both  the  lateral  slopes  and  the  fold  and  sinus.  Besides  the  plica- 
tions the  surface  may  also  be  marked  by  fine,  radiating  striae  or  by  fine 
or  coarse  concentric  growth  lines,  or  by  both  radiating  and  concentric 
markings.  The  pedicle  valve  with  the  beak  variously  elevated  above 
the  hinge-line  and  variously  incurved,  the  cardinal  area  varying  from 
very  narrow  to  high,  usually  arched  but  sometimes  nearly  or  quite  flat, 
the  delthyrium  rather  broadly  triangular  and  open ;  the  surface  of  the 
cardinal  area  is  transversely  striate  and  the  inner  shell  layers  bear  a 
series  of  vertical  canals  at  whose  extremities  along  the  hinge-line  the 
shell  tissue  is  sometimes  produced  in  a  row  of  denticles  which  articulate 
with  a  row  of  pits  in  the  opposite  valve.  Internally  the  hinge-teeth  are 
strong  and  are  supported  by  short  dental  lamella1;  the  muscular  area 
is  of  moderate  size  and  is  often  deeply  impressed,  ovate  or  obcordate  in 
outline,  occupied  in  large  part  by  the  diductor  scars  which  are  usually 
marked  by  radiating  or  branching  furrows.  The  brachial  valve  with  a 
very  narrow  cardinal  area  divided  by  a  broadly  triangular  delthyrium ; 
the  cardinal  process  is  a  low,  transverse,  sessile  apophysis  with  its  surface 


308 


MISSISSIPPIAN    BKAGHIOPODA 


vertically  striated;  the  muscular  impressions  much  less  strongly  marked 
than  in  the  pedicle  valve;  the  dental  sockets  narrow  and  of  moderate 
depth,  the  socket  plates  well  developed  and  at  their  extremities  sup- 
porting the  crural  bases;  the  crura  are  long,  straight,  and  slightly  diverg- 
ent, the  spiral  cones  are  directed  obliquely  outward  and  posteriorly 
towards  the  cardinal  extremities,  the  primary  lamellae  are  not  united  by  a 
jugnm,  hut  the  position  of  the  jngnm  is  indicated  by  the  presence  of  a 
paii-  of  spine-like  processes  upon  the  primary  lamella'  a  little  in  front  of 
their  junction  with  the  crura. 

Remarks. — This  genus  has  the  largest  specific  representation  of  any  in 
our  Mississippian  faunas,  and  the  species  themselves  are  usually  very 
characteristic  of  the  horizon  in  which  they  oecur.  As  a  whole  the  Missis- 
sippian species  are  characterized  by  the  presence  of  plications  in  the  fold 
and  sinus  of  the  valves,  and  in  a  large  number  of  the  species  the  plica- 
tions upon  the  lateral  slopes  exhibit  more  or  less  bifurcation. 


Spirifer  marionensis  Shumard 
Plate  XXXV11,  Figs.  1-7 

IS.").").     Spirifer  Marionensis  Shumard,  Geol.  Hep.  Mo.,  1855,  p.  203,  pi.  C, 

figs.  Sa-b   ( not  fig.  8c). 
1858.     Spirifer  marionensis  Hall.  Geol.  Surv.  Iowa,  vol.  1,  pt.  2,  p.  511, 

pi.  ti,  figs,  la-e. 
1883.     Spirifera  Marionensis  Hall.  2nd  Ann.  Rep.  N.  Y.  State  Geol.,  pi. 

(31)  56,  fig.  15. 
1894.     Spirifer  Marionensis  Hall  and  Clarke,  13th  Ann.  Rep.  N.  Y.  State 

Geol.,  vol.  2.  pi.  27,  fig.  3. 

1894.  Spirifera  marionensis  Keye<,  Mo.  Geol.  Surv.,  vol.  5,  p.  78,  pi.  40, 

figs.  la-b. 

1895.  Spirifer  Marionensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  31, 

fig.  15. 
1908.     Spirifer  marionensis  Rowlev,  Mo.  'Bureau  Geol.  and  Mines,  vol.  8, 
2nd  ser.,  p.  81,  pi.  18,  figs'  1-5 ;  p.  88,  pi.  19,  figs.  3-6. 

Description. — Shell  of  medium  size,  subsemicircular  to  subtriangular  in 
outline,  greatest  width  usually  along  the  hinge-line,  cardinal  extremities 
acutely  angular  in  immature  shells,  the  hinge-line  becoming  relatively 
shorter  and  the  cardinal  extremities  more  obtuse  with  age.  The  dimen- 
sions of  an  average  specimen  are :  length  of  pedicle  valve  24  mm.,  length 
of  brachial  valve  20  mm.,  width  along  hinge-line  39  mm.,  thickness  17  mm., 
height  of  cardinal  area  3  mm. 

Pedicle  valve  moderately  convex,  usually  becoming  compressed  towards 
the  cardinal  extremities,  the  umbonal  region  rather  narrow,  the  surface 
curving  abruptly  from  it  to  the  cardinal  margin  for  a  short  distance  on 
each  side  of  the  beak,  the  slope  more  gentle  to  the  antero-lateral  margins; 
beak  small,  pointed,  and  incurved;  cardinal  area  of  moderate  height, 
arched,  the  curvature  increasing  towards  the  beak,    the    lateral  margins 


SPIRIFER  309 

sharply  defined,  subparallel  with  the  cardinal  margin  through  nearly  the 
entire  length  of  the  area,  the  lateral  extremities  of  the  area  abruptly 
truncate,  its  surface  both  longitudinally  and  vertically  striate;  lateral 
slopes  of  the  valve  convex  towards  the  middle,  often  with  an  obscure 
oblique  sinuosity  extending  from  the  side  of  the  umbonal  region  to  just 
in  front  of  the  cardinal  extremities,  each  marked  by  about  20  rounded 
plications,  the  first  two  or  three  of  which  adjacent  to  the  sinus  usually 
bifurcate  in  passing  to  the  anterior  margin,  the  other  plications  remain- 
ing simple ;  mesial  sinus  originating  at  the  beak  where  it  is  sharply  de- 
fined, becoming  less  sharply  defined  anteriorly,  it  is  shallow  and  rounded 
in  the  bottom,  a  median  plication  originates  near  the  beak  and  passes 
without  division  to  the  anterior  margin,  on  each  side  there  are  usually 
two  lateral  plications  originating  from  the  inner  margins  of  the  bounding 
plications,  all  the  plications  of  the  sinus  being  similar  in  form  and  size  to 
those  of  the  lateral  slopes. 

Brachial  valve  slightly  less  convex  than  the  pedicle,  with  a  narrow, 
linear  cardinal  area,  the  greatest  convexity  of  the  valve  near  or  posterior 
to  the  middle ;  mesial  fold  originating  at  the  beak  where  it  is  bounded  by 
furrows  deeper  than  those  between  the  other  plications  of  the  shell,  not 
at  all  or  but  little  elevated  above  the  general  surface  of  the  shell  in  the 
umbonal  region,  and  but  slightly  elevated  anteriorly,  it  is  rounded  in  con- 
tour and  is  marked  by  plications  similar  in  form  and  number  to  those  of 
the  mesial  sinus  of  the  other  valve,  all  of  which  originate  through  the 
division  of  a  single  plication  at  the  beak ;  lateral  slopes  moderately  con- 
vex antero-posteriorly,  the  curvature  more  abrupt  towards  the  cardinal 
margin,  the  surface  somewhat  compressed  towards  the  cardinal  extremi- 
ties, marked  by  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve. 

The  minute  surface  markings  consist  of  fine  concentric  striae  which  are 
crowded  at  intervals  to  form  more  or  less  conspicuous,  irregularly  ar- 
ranged lines  of  growth  which  are  often  crowded  towards  the  anterior 
margin. 

Remarks. — This  species  resembles  several  other  Kinderhook  members 
of  the  genus  Spirifer,  but  it  may  always  be  distinguished  by  the  form  of 
the  cardinal  area  of  the  pedicle  valve,  the  two  margins  of  the  area  being 
essentially  parallel  almost  to  their  very  extremities,  giving  to  the  area 
the  form  of  a  long,  narrow  parallelogram,  while  in  the  allied  species  the 
lateral  margins  of  the  area  slope  laterally  towards  the  hinge-line,  giving 
to  the  area  a  broadly  triangular  outline.  From  S.  vernonensis,  the  species 
may  also  be  distinguished  by  its  less  convex  valves  and  less  prominent 
fold  and  sinus. 

The  manner  of  growth  which  produces  the  characteristic  form  of  car- 
dinal area  of  this  species  is  peculiar.  In  the  younger  growth  stages  of  the 
shell  the  hinge-line  is  much  extended  into  mucronate  points,  so  that  when 


310 


MISSISSIPPI  \\    KUACIIIUI'ODA 


the  shell  lias  reached  one-third  of  its  mature  size  the  hinge-line  has 

leached  nearly  its  maximum  Length,  with  a  very  narrow  cardinal  area. 
During  the  more  mature  growth  of  the  shell  the  length  of  the  hinge-line 
remains  stationary,  while  the  shell  itself  increases  in  length  and  the  car- 
dinal area  increases  in  height.  In  rare  instances  the  elongation  of  the 
hinge-line  is  retarded  still  earlier  in  the  life  of  the  individual  so  that  as 
the  shell  increases  in  size  the  greatest  width  is  not  along  the  hinge-lhie, 
hut  is  in  front  of  this  line  and  the  cardinal  extremities  become  rounded  in 
the  mature  shell. 

This  species  is  especially  characteristic  of  the  fauna  of  the  Louisiana 
limestone.  In  the  original  description  of  the  species  it  was  said  to  occur 
also  in  the  Chouteau  limestone  of  central  Missouri,  and  it  has  been  fre- 
quently identified  by  later  authors  from  various  Kinderhook  localities 
and  horizons.  All  of  these  identifications,  however,  are  believed  to  be  in- 
correct. Aside  from  in  the  Louisiana  limestone,  the  species  has  been 
recognized  by  the  writer  only  in  the  yellow  Kinderhook  sandstone  at 
Kinderhook,  Illinois.  The  specimens  from  this  locality  are  all  imperfect 
and  more  or  less  poorly  preserved.  They  seem  to  attain  a  somewhat 
larger  size  than  the  Louisiana  limestone  specimens,  and  in  none  of  them 
has  the  form  of  the  cardinal  area  been  actually  observed.  The  sand- 
stone specimens  exhibit  the  shallow  sinus  and  low  fold  of  the  typical 
members  of  the  species,  and  the  lines  of  growth  seem  to  indicate  the  early 
attainment  of  the  maximum  length  of  the  hinge-line  during  the  growth 
of  the  shell,  and  for  these  reasons  the  specimens  are  provisionally  referred 
to  this  species. 

Horizon. — Louisiana  limestone. 


Spirifer  vernonensis  Swallow 
Plate  XXXVII,  Figs.  8-17 

I860.     Spirifer  vernonensis,  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1. 

p.  644. 
1865.     Spirifer  Vt  rnomnsis  Winchell,  Proe.  Acad.  Nat.  Sci.  Phil.,  p.  119. 
1909.     Spirifer  vernonensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  302, 

pi.  13,  figs.  3-8. 

Description. — Shell  of  medium  size,  subsemicircular  in  outline,  wider 
than  long,  the  greatest  width  along  the  hinge-line,  cardinal  extremities 
angular.  The  dimensions  of  two  individuals  are :  length  of  pedicle  valve 
23  mm.  and  25  mm.,  length  of  brachial  valve  17.5  mm.  and  20.5  mm.,  width 
31  mm.  and  43  mm.,  thickness  19  mm.  and  22  mm.,  height  of  cardinal  area 
3.5  mm.  and  3.5  mm. 

Pedicle  valve  strongly  convex,  strongly  arched  from  the  beak  to  the 
front,  the  median  line  often  describing  nearly  a  semicircle;  beak  small, 
pointed,  strongly  incurved;  cardinal   area   of  moderate  height,   arched. 


SPIBIPER  311 

the  curvature  becoming  stronger  towards  the  beak,  the  lateral  margins 
sharply  defined,  sloping  from  the  beak  to  the  cardinal  extremities  with  a 
convex  curve  which  becomes  more  abrupt  as  it  approaches  the  end,  the 
surface  marked  by  vertical  stria'  and  by  fine  longitudinal  lines  of  growth, 
hinge-line  finely  crenulate;  lateral  slopes  convex  throughout  the  greater 
portion  of  their  area,  becoming  more  or  less  compressed  towards  the  car- 
dinal extremities,  often  with  a  slight  sinuosity  passing  obliquely  from  the 
side  of  the  umbo  to  just  in  front  of  the  cardinal  extremity,  each  marked 
by  from  15  to  18  subangular  or  rounded,  mostly  simple,  but  rarely  bifur- 
cating plications  which  grow  progressively  smaller  towards  the  cardinal 
extremities;  mesial  sinus  sharply  defined  at  the  beak  and  losing  but  little 
of  its  definition  anteriorly,  it  is  rather  deep  and  subangular  or  rounded 
in  the  bottom,  with  a  conspicuous  lingual  prolongation  in  front,  it  is 
marked  by  a  median  plication  which  originates  near  the  beak  and  con- 
tinues without  division  to  the  anterior  margin,  each  side  is  marked  by 
three  or  four  lateral  plications  which  originate  successively  from  the  inner 
margins  of  the  lateral  bounding  plications. 

Brachial  valve  nearly  as  convex  as  the  pedicle,  most  elevated  at  or  near 
the  anterior  extremity  of  the  mesial  fold,  with  a  narrow,  linear  cardinal 
area ;  mesial  fold  sharply  defined  to  the  beak  by  a  pair  of  furrows  deeper 
than  those  between  the  other  plications,  depressed  and  but  slightly  ele- 
vated above  the  general  surface  of  the  valve  posteriorly,  becoming 
strongly  elevated  and  sometimes  slightly  recurved  towards  the  anterior 
margin,  simple  at  the  beak  but  marked  anteriorly  by  8  or  10  plications 
which  originate  through  the  successive  bifurcation  of  the  original  me- 
dian ridge;  lateral  slopes  convex  towards  the  center  of  the  shell,  the 
curvature  more  abrupt  to  the  cardinal  margin,  becoming  somewhat  com- 
pressed towards  the  cardinal  extremities. 

The  entire  surface  of  the  shell  is  marked  by  fine,  concentric,  sublamel- 
lose  lines  which  are  crowded  at  intervals,  especially  towards  the  front,  to 
form  more  or  less  conspicuous  lines  of  growth. 

Remarks.— This  species  resembles  S.  marionensis,  but  it  is  much  more 
convex  in  both  valves,  with  a  much  more  elevated  mesial  fold  and  de- 
pressed sinus  anteriorly.  The  shape  of  the  cardinal  area  of  the  pedicle 
valve  is  also  different,  the  lateral  margins  sloping  laterally  towards  the 
cardinal  extremities,  while  in  S.  marionensis  the  two  margins  of  the  area 
are  essentially  parallel.  The  manner  of  growth  of  the  shell  of  this  species 
is  accountable  for  the  difference  in  the  form  of  the  cardinal  area  from  that 
of  S.  marionensis.  The  length  of  the  hinge-line  continues  to  increase 
throughout  the  entire  period  of  growth  of  the  shell,  although  as  the  shell 
approaches  maturity,  the  elongation  is  proportionally  less  rapid ;  at  the 
same  time  the  height  of  the  cardinal  area  is  continually  increasing  so  that 
the  mature  shell  possesses  the  broadly  subtriangular  cardinal  area. 

Horizon. — Fern  Glen  formation. 


312 


MISSISSIPPIAN    HUACIIIill-IIDA 


Spibifeb  pikensis  Rowley 
Plate  XXXVIII,  Figs.  1-5 
1902.    Spirift  r  pikensis  Elowley,  Am.  Geol.,  vol.  29,  p.  309,  pi.  18,  figs.  17-22. 

Description.— Shell  large,  broader  than  long,  the  hinge-line  a  little 
shorter  than  the  greatest  width,  the  cardinal  extremities  ohtusely  angular. 
The  dimensions  of  a  nearly  perfed  specimen,  the  holotype,  are:  length 
of  pedicle  valve  62  mm.,  length  of  brachial  valve  53.4  mm.,  greatest 
width  80.5  nun.,  thickness  :i(>  mm.,  length  of  hinge-line  To  mm.,  height,  of 
cardinal  area  5  mm. 

Pedicle  valve  moderately  convex,  the  surface  curving  abruptly  from 
the  umhoiial  region  to  the  cardinal  margin  on  each  side  of  the  beak,  and 
sloping  with  a  gently  convex  curve  to  the  Lateral  and  antero-lateral  mar- 
gins, only  slightly  compressed  towards  the  cardinal  extremities;  mesial 
sinus  originating  at  the  beak  where  it  is  narrow,  angular  and  rather 
sharply  defined,  less  well  defined  anteriorly  where  it  is  narrowly  rounded 
in  the  bottom  and  rapidly  increases  in  depth,  becoming  profound  towards 
the  anterior  margin,  greatly  produced  in  front  in  a  conspicuous  lingual 
extension  which  is  narrowly  rounded  at  its  extremity;  the  beak  rather 
small  and  pointed,  moderately  incurved  at  the  apex;  cardinal  area  rather 
low,  gently  concave  except  just  under  the  beak,  where  the  curvature 
becomes  much  stronger,  the  lateral  margins  sharply  denned  and  sloping 
with  a  gentle  curvature  from  the  beak  to  the  cardinal  extremities,  the 
delthyrium  rather  small,  broader  than  high.  Surface  of  the  valve  marked 
by  rounded,  radiating  plications  which  occupy  the  lateral  slopes  and  the 
mesial  sinus,  the  largest  plications  occur  upon  the  lateral  slopes  adjacent 
to  the  sinus  where  they  sometimes  measure  3  mm.  from  center  to  center 
at  the  front  margin,  towards  the  cardinal  extremities  they  gradually 
decrease  in  size,  about  25  being  present  upon  each  lateral  slope,  about  16 
occupy  the  sinus,  all  the  larger  plications  bifurcate  once  or  sometimes 
twice  near  the  beak,  with  an  occasional  bifurcation  further  towards  the 
front,  sometimes  in  front  of  the  middle  of  the  valve. 

Brachial  valve  more  convex  than  the  pedicle,  its  greatest  depth  at  the 
front  of  the  mesial  fold,  surface  of  the  valve  sloping  posteriorly  from 
the  point  of  greatest  convexity  along  the  median  line  in  nearly  a  straight 
line  for  about  two-thirds  the  length  of  the  valve,  from  which  point  it  is 
convexly  curved  to  the  beak;  from  the  median  line  the  surface  curves 
abruptly  on  either  side  anteriorly,  to  the  lateral  borders  of  the  mesial 
fold,  beyond  which  lines  the  surface  is  gently  convex,  becoming  some- 
what compressed  towards  the  cardinal  extremities,  curving  more  ab- 
ruptly to  the  cardinal  margin  on  either  side  of  the  beak;  mesial  fold 
only  slightly  elevated  near  the  beak,  but  rapidly  becoming  highly  elevated 
in  the  anterior  half  of  the  valve  where  it  is  narrowly  rounded  across 
the  top;  beak  small  and  rather  strongly  incurved,  the  umbonal  region 


SPIRIFER  313 

only  slightly  protuberant  beyond  the  hinge-line.  Surface  marked  by 
plications  similar  in  form  and  number  to  those  of  the  opposite  valve, 
those  of  the  mesial  fold  becoming  much  broader  and  less  elevated 
towards  the  front  than  those  of  the  lateral  slopes. 

A  few  rather  faint  lines  of  growth  are  present  upon  each  valve,  the 
finer  surface  markings  not  preserved  upon  the  type  specimen. 

Ri  marks. — This  species  is  especially  characterized  by  the  extreme  de- 
velopment of  the  fold  and  sinus  near  the  front  of  the  shell,  no  other 
species  being  present  in  our  faunas  which  is  at  all  comparable  in  this  re- 
spect. Another  distinguishing  character  is  to  be  found  in  the  bifurcation 
of  the  plications  and  their  unusual  width  towards  the  front. 

Horizon. — Burlington  limestone. 

Spirifer  shepardi  n.  sp. 
Plate  XXXVIIJ,  Figs.  6-8 

Description. — Shell  of  medium  size,  subsemieircular  in  outline,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  angular, 
sometimes  mucronate.  The  dimensions  of  a  nearly  perfect  pedicle  valve 
are :  length  21  mm.,  width  along  hinge-line  40.5  mm.,  convexity  12.5  mm., 
height  of  cardinal  area  5  mm.  The  dimensions  of  a  somewhat  imperfect 
brachial  valve  are :  length  20  mm.,  approximate  width  36  mm.,  con- 
vexity 7  mm. 

Pedicle  valve  rather  strongly  convex,  greatest  convexity  posterior  to 
the  middle,  the  surface  curving  abruptly  from  the  umbonal  region  to 
the  cardinal  margin  and  more  gently  to  the  anterolateral  margins, 
usually  a  little  compressed  towards  the  cardinal  extremities,  sometimes 
with  an  ill-defined  sinuosity  passing  obliquely  from  each  side  of  the  beak 
to  the  lateral  margins  just  in  front  of  the  cardinal  extremities ;  beak 
small,  pointed,  incurved;  cardinal  area  of  moderate  height,  arched,  the 
curvature  increasing  towards  the  beak,  lateral  margins  sharply  defined, 
sloping  from  the  beak  to  the  cardinal  extremities ;  lateral  slopes  marked 
by  from  20  to  23  rounded  plications,  the  first  two  or  three  on  each  side 
of  the  fold  and  sinus  may  bifurcate,  the  others  simple,  towards 
the  cardinal  extremities  the  plications  become  successively  weaker,  the 
last  two  or  three  being  sometimes  very  faint  or  obsolete ;  mesial  sinus  of 
moderate  depth,  rounded  or  subangular  in  the  bottom,  sharply  defined 
to  the  beak,  somewhat  loosing  its  definition  anteriorly,  but  slightly  pro- 
duced in  front,  marked  by  a  median  plication  which  originates  near  the 
beak  and  passes  to  the  anterior  margin  either  without  division  or  bifurcat- 
ing, on  each  side  there  are  from  two  to  four  plications  which  originate 
from  the  inner  margins  of  the  lateral  bounding  plications  or  through  the 
bifurcation  of  plications  so  originating,  making  usually  from  7  to  !> 
plications  in  all. 


■11  MISSISSIPPIAN    BRACHIOPODA 

Brachial  valve  depressed  convex,  usually  much  Less  convex  than  the 
pedicle  valve,  the  greatest  convexity  near  or  posterior  to  the  middle,  the 
surface   somewhat    compressed   towards   the   cardinal    extremities;    mesial 

fold    depressed,    usually    not    elevated    aliove    the    general    surface    of    the 

valve  posteriorly  and  hut  slightly  elevated  anteriorly,  hounded  by  a  pair 
of  furrows  somewhat  deeper  and  stronger  than  those  between  the  plica- 
tions, marked  by  plications  similar  in  form  and  number  to  those  of  the 
sinus  of  the  opposite  valve,  all  of  which  originate  through  the  division  of 
a  single  one  at  the  beak;  lateral  slopes  convex  towards  the  middle  of  the 
valve,  the  curvature  more  abrupt  towards  (lie  cardinal  margin,  com- 
pressed towards  the  cardinal  extremities,  marked  by  plications  similar 
in   form  and  number  to  those  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  fine,  concentric,  subimbricating  lines 
which  arc  crowded  at  intervals  to  form  lines  of  growth  of  greater  or 
less  strength. 

/.'i  marks.  —  This  species  has  sometimes  been  identified  as  8.  marionensis, 
hut  it  is  quite  different  from  that  species,  being  more  closely  allied  to 
8.  vernonensis.  It  differs  from  8.  vernonensis,  however,  in  being  marked 
by  more  numerous  and  liner  plications,  those  upon  the  fold  and  sinus 
being  equally  prominent  with  those  upon  the  lateral  slopes,  in  not  having 
the  sinus  of  the  pedicle  valve  produced  anteriorly  and  consequently 
lacking  the  strongly  elevated  fold  of  the  brachial  valve.  It  differs  from 
8.  osagensis  in  its  larger  size,  its  more  numerous  and  sometimes  bifurcating 
plications  upon  the  lateral  slopes,  and  in  the  larger  number  of  plications 
upon  the  fold  and  sinus.  The  species  is  in  some  respects  intermediate  in 
character  between  S.  vernonensis  and  8.  csagensis. 

Horizon. — Pierson  limestone  of  the  Kinderhook. 

Spirifee  osagensis  Swallow 

Plate  XXXVII,  Figs.  18-21 

1860.     Spirifer  osagensis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1,  p.  641. 
1899.     Spirifer  marionensis  AVeller,   Trans.   St.  Louis  Acad.   Sci.,  vol.  9, 
p.  17,  pi.  4,  fig.  12. 

Description.  —  Shell  of  medium  size  or  smaller,  submenu  circular  or  sub- 
semielliptical  in  outline,  the  greatest  width  along  the  hinge-line,  the 
cardinal  extremities  mucronate.  The  dimensions  of  two  rather  small  but, 
nearly  complete  individuals  with  the  mucronate  cardinal  extremities  de- 
stroyed are:  length  of  pedicle  valve  16.5  mm.  and  15.5  mm.,  length  of 
brachial  valve  15.3  mm.  and  14.8  mm.,  width,  exclusive  of  cardinal  ex- 
tremities, 22  mm.  and  19.5  mm.,  thickness  13  mm.  and  12.5  mm.,  height 
of  cardinal'area  2.5  mm.  and  2.3  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  umbonal  region  prominent,  the  surface  curving  abruptly 


M'IKIFER  315 

to  the  cardinal  margin  on  each  side  of  the  beak,  to  the  antero-lateral 
margins  the  curvature  is  more  gentle,  an  ill-defined  oblique  sinuosity 
passes  from  the  cardinal  margin  on  each  side  of  the  beak  to  just  in  front 
of  the  cardinal  extremities,  the  valve  sometimes  a  little  compressed 
towards  the  cardinal  extremities ;  beak  rather  small,  pointed,  incurved ; 
cardinal  area  rather  low,  arched,  the  curvature  becoming  greater  towards 
the  beak,  lateral  margins  sharply  defined,  sloping  from  the  beak  to  the 
cardinal  extremities  in  a  nearly  straight  line  or  with  a  gently  convex 
curve,  surface  of  the  area  vertically  striate;  lateral  slopes  convex 
towards  the  mesial  sinus,  visually  slightly  compressed  towards  the  cardinal 
extremities,  marked  by  from  13  to  15  simple,  rounded  plications  which 
grow  successively  smaller  towards  the  cardinal  extremities,  the  last  two 
or  three  sometimes  being  very  faint  or  almost  obsolete;  mesial  sinus 
originating  at  the  beak  where  it  is  sharply  defined,  becoming  less  sharply 
defined  anteriorly,  it  is  rather  shallow  and  rounded  or  subangular  in 
the  bottom,  marked  by  a  median  plication  which  originates  near  the  beak 
and  passes  without  division  to  the  anterior  margin,  on  each  side  are  from 
1  to  3,  but  mostly  2,  lateral  plications  which  originate  from  the  inner 
margins  of  the  lateral  bounding  plications. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  or  posterior  to  the  middle;  mesial  fold  sharply  defined  to  the 
beak,  the  bounding  furrows  deeper  and  stronger  than  those  between 
the  other  plications,  but  little  or  not  at  all  elevated  in  the  posterior  half 
of  the  shell,  becoming  slightly  elevated  anteriorly ;  it  is  marked  anteriorly 
by  plications  similar  in  form  and  number  to  those  of  the  sinus  of  the 
opposite  valve,  all  of  which  originate  through  the  division  of  a  single 
plication  at  the  beak ;  lateral  slopes  convex  towards  the  middle  of  the 
valve,  becoming  compressed  towards  the  cardinal  extremities,  marked  by 
plications  similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  are  obscure  in  all  of  the  specimens  ex- 
amined because  of  the  condition  of  preservation,  but  concentric  markings 
of  the  shell  are  clearly  indicated  which  are  sometimes  crowded  into 
more  or  less  conspicuous  lines  of  growth. 

Remarks. — This  species  has  sometimes  been  identified  as  S.  marionemis, 
but  it  differs  markedly  from  that  species  in  the  shape  of  the  cardinal 
area  and  also  in  the  absence  of  bifurcating  plications  upon  the  lateral 
slopes.  From  S.  vernonensis  it  differs  in  the  less  strongly  convex  valves, 
in  the  shallower  sinus,  and  in  the  absence  of  the  conspicuous  lingual 
extension  in  front,  and  in  the  lower  mesial  fold,  also  in  the  mucronate 
extensions  of  the  hinge-line.  These  mucronate  extensions  are  frequently 
missing  on  the  specimens  as  they  occur  in  the  form  of  more  or  less  im- 
perfect casts,  but  in  every  specimen  in  which  this  portion  of  the  shell 
is  uninjured,  they  have  been  observed,  and  it  is  believed  that  the  character 


•>l(i  MISSISS1PPIAN    BRACHIOPODA 

is  n  constant  one.  The  younger  individuals  of  S.  marionensis  possess 
siiiiihir  tnucronate  cardinal  extremities,  bu1  the  hinge-line  docs  not  con- 
tinue  to  increase  in  length  through  the  entire  life  of  the  individual  as 
it  docs  in  8.  osagt  nsis. 

The  shell  illustrated  by  Meek  from  the  Ohio  Waverly  as  8.  biplicatus* 
resembles  tins  one  very  closely  in  general  form  and  size  and  may  be 
identical,  it  is  certainly  entirely  different  from  the  true  8.  biplicatus.  Well 
preserved  examples  of  this  shell  from  Licking  County,  Ohio,  preserve  the 
minute,  surface  characters  perfectly,  which  consist  of  fine,  exceedingly 
regular,  concentric  marks,  which  are  crossed  by  still  liner  radiating  striae, 
giving  the  surface  a  xi'vy  beautiful  reticulate  appearance.  None  of  the 
Missouri  examples  of  8.  osagensis  are  preserved  so  as  to  show  such  mark- 
ings, hut  if  they  should  he  present  the  identity  of  the  Ohio  shells  is  more 
sure. 

Horizon. — Kinderhook. 

Spiriper  latior  Swallow 
L'late  XXXVIII.  Figs.  9-13 
1863.     Spirifer  latior  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2,  p.  86. 

Description. — Shell  small,  subsemicircular  in  outline,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimensions  of 
a  nearly  perfect  specimen  are:  length  of  pedicle  valve  12.5  mm.,  length 
of  brachial  valve  10  mm.,  width  along  hinge-line  15.5  mm.,  thickness  9 
mm.,  height  of  cardinal  area  2.5  mm. 

Pedicle  valve  rather  strongly  convex  with  the  greatest  convexity 
posterior  to  the  middle  and  well  towards  the  umbo,  the  surface  curving 
abruptly  to  the  cardinal  margin,  the  slopes  from  the  umbo  to  the 
cardinal  extremities  at  first  gently  convex,  becoming  a  little  concave 
towards  the  cardinal  extremities,  to  the  anterior  and  antero-lateral 
margins  the  curvature  is. gently  convex;  beak  small,  pointed  and  in- 
curved ;  cardinal  area  of  moderate  height,  concave,  the  lateral  margins 
sharply  defined  and  sloping  from  the  sides  of  the  beak  to  the  cardinal 
extremities;  mesial  sinus  originating  at  the  beak  as  a  narrow,  sharply 
defined  groove-like  depression  becoming  broader  and  ill-defined  anter- 
iorly where  it  is  rather  shallow  and  rounded  in  the  bottom,  a  rounded 
median  plication  originates  in  the  umbonal  region  and  continues  to  the 
front  without  subdivision,  upon  each  side  of  the  median  one  there  is  a 
single  similar  plication  which  originates  from  the  inner  margin  of  the 
bounding  plications  of  the  sinus ;  each  lateral  slope  of  the  valve  marked 
by  12  to  15  simple,  rounded  plications  which  decrease  regularly  in  size 
towards  the  cardinal  extremities. 

l  Spirifer  Mplicatus  ?  Meek,  Pal.  Ohio,  vol.  2,  p.  290,  pi.  14,  fig.  5  (1875). 


SPIRIPER  317 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  depth  a  little 
posterior  to  the  middle,  becoming  a  little  compressed  towards  the  car- 
dinal extremities ;  cardinal  area  very  narrow  and  linear ;  mesial  fold 
originating  at  the  beak,  where  it  is  bounded  by  rather  strong  furrows  but 
is  not  elevated  above  the  surface  of  the  valve  on  either  side,  anteriorly 
it  continues  to  be  sharply  defined  by  the  stronger  furrows  but  is  con- 
spicuously depressed  to  the  front,  being  scarcely  elevated  above  the 
surface  of  the  lateral  slopes,  it  is  marked  by  four  subequal,  rounded 
plications,  all  of  which  originate  through  the  subdivision  of  the  original 
07ie  at  the  beak ;  each  lateral  slope  marked  by  simple  plications  which 
are  entirely  similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  are  not  well  preserved  upon  the  specimens 
observed,  but  the  concentric  lines  of  growth  are  inconspicuous,  com- 
monly being  restricted  to  a  few  faint  ones  near  the  margin  of  the  shell. 

Remarks, — The  original  type  of  this  species  was  never  illustrated  and 
the  specimen  itself  has  been  lost,  and  from  the  original  definition  alone 
it  would  be  difficult  to  determine  the  status  of  the  species.  In  the  col- 
lection of  Mr.  D.  K.  Greger,  however,  a  specimen  is  preserved  accom- 
panied by  a  label  written  by  Swallow  himself.  This  specimen  is  con- 
sidered to  be  authentic  and  it  agrees  in  all  essential  respects  with  the 
original  definition.  The  specimen  which  is  illustrated  herewith,  and 
which  has  been  used  in  the  preparation  of  the  above  description,  agrees 
in  all  essential  respects  with  the  authentic  example  in  the  Greger  col- 
lection. The  species  is  a  small  one,  although  it  grows  considerably 
larger  than  the  specimen  whose  dimensions  have  been  given,  and  is 
characterized  especially  by  its  rotund  form,  there  being  little  or  no 
compression  of  the  pedicle  valve  towards  the  cardinal  extremities,  and 
the  mesial  fold  of  the  brachial  valve  being  depressed  to  such  a  degree 
that  it  scarcely  interrupts  the  general  convexity  of  that  valve.  The 
species  is  evidently  not  a  common  form. 

Horizon. — Chouteau  limestone. 

Spirifer  platynotus  n.  sp. 
Plate  XXXIX,  Figs.  1-10 

1901.     Spirifer  marionensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
p.  188,  i>l.  16,  figs.  16-17. 

Description. — Shell  below  medium  size,  subsemieircular  to  broadly 
sub-triangular  in  outline,  greatest  width  along  the  hinge-line,  cardinal 
extremities  more  or  less  acutely  angular.  The  dimensions  of  two  pedicle 
valves  are :  length  16  mm.  and  15.5  mm.,  width  along  the  hinge-line 
25  mm.  and  ±42  mm.,  convexity  8  mm.  and  7.5  mm.,  height  of  cardinal 
area  3.5  mm.  and  3.5  mm.  The  dimensions  of  a  brachial  valve  are:  length 
16  mm.,  width  along  the  hinge-line  ±38  mm.,  convexity  6.5  mm. 


il8  MISSISS1PPIAN   BRACHIOPODA 

Pedicle  valve  most  convex  posterior  to  (he  middle,  the  surface  curving 
abruptly  from  the  umbonal  region  to  the  cardinal  margin  on  each  side 
of  the  beak,  Curving  more  gently  to  the  anterodateral  margins  and 
becoming  compressed  towards  the  cardinal  extremities;  beak  small, 
pointed,  moderately  incurved;  cardinal  area  of  moderate  height,  arched, 
the  curvature  slight  in  the  inferior  portion,  becoming  stronger  towards 
the  beak.  Lateral  margins  sharply  defined,  sloping  from  the  beak  to 
the  cardinal  extremities,  the  slope  becoming  more  abrupt  distally, 
surface  marked  bj  vertical  lines,  the  hinge-margin  minutely  crennlate, 
the  delthyrium  Large,  broadly  triangular;  Lateral  slopes  convex  towards 
the  middle  of  the  valve,  becoming  compressed  towards  the  cardinal 
extremities,  each  marked  by  from  16  to  20  depressed  rounded  plications 
which  grow  successively  fainter  towards  the  cardinal  extremities,  in 
those  individuals  with  excessively  elongate  hingedines  becoming  nearly 
or  quite  obsolete  distally,  the  first  one  or  two  plications  on  each  side 
of  the  sinus  bifurcate  close  to  the  beak,  the  remaining  ones  are  simple; 
mesial   sinus  shallow,   rounded    in   the   bottom,   defined  to  the  beak,   be- 

i ling  less  sharply  defined   anteriorly,  marked  by  a  median  plication 

which  originates  near  the  beak  and  passes  to  the  anterior  margin  either 
as  a  simple  plication  or  bifurcating  near  the  middle  of  the  valve,  on  each 
side  are  one,  or  more  rarely  two,  plications  which  originate  from  the 
inner  margin  of  the  bounding  plications. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
the  middle,  the  surface  curving  more  abruptly  to  the  cardinal  margin, 
compressed  towards  the  cardinal  extremities ;  mesial  fold  defined  from 
the  beak  to  the  front  by  a  pair  of  furrows  which  are  deeper  and  stronger 
than  those  between  the  plications,  scarcely  or  not  at  all  elevated  above 
the  general  surface  of  the  valve  through  its  entire  extent,  marked  by  four 
or  five  plications  similar  to  those  on  the  lateral  slopes  which  originate 
from  a  single  one  at  the  beak;  lateral  slopes  marked  by  plications  similar 
in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  consist  of  exceedingly  fine  concentric 
striae  which  are  sometimes  crowded  at  intervals,  and  especially  towards 
the  anterior  margin,  to  form  more  or  less  conspicuous  lines  of  growth. 

Remarks. — This  species  is  especially  characterized  by  the  great  variation 
it  exhibits  in  the  length  of  the  hinge  line,  and  in  the  complete,  or  almost 
complete,  lack  of  elevation  of  the  mesial  fold  of  the  brachial  valve  above 
the  general  surface  of  the  valve.  The  pedicle  valve  often  more  or  less 
closely  resembles  that  of  S.  osagensis,  but  the  plications  are  finer  and  more 
numerous,  and  the  hinge-line  is  apt  to  be  more  elongate,  the  brachial 
valves  of  the  two  species  are  less  alike. 

The  types  of  this  species  are  all  from  the  white  oolitic  bed.  No.  6  of 
the  Kinderhook  section  at  Burlington,  Iowa,  but  some  specimens  in  the 
yellowr  sandstone  bed,  No.  5,  just  below,  and  in  the  superjacent  bed,  No.  7, 


SPIRIFER  319 

seem   to  represent   the  same  species.      The    specimens  from   both  these 
horizons  seem  to  be  more  uniformly  elongate  along  the  hinge-line,  and 
none  of  those  observed  attain  so  large  a  size    as    is    common  among  the 
examples  from  the  oolite. 
Horizon. — Kinderhook. 

Spirifer  missouriensis  Swallow- 
Plate  XXXIX,  Figs.  11-23 

1860.     Spirifer  Missouriensis  Swallow.  Trans.  St.  Louis  Acad.  Sci..  vol.  1. 
p.  643. 

Description.— Shell  of  medium  size  or  smaller,  wider  than  long,  the 
greatest  width  along  the  hinge-line,  cardinal  extremities  angular,  the  pli- 
cations of  the  fold  and  sinus  similar  to  those  of  the  lateral  slopes.  The 
dimensions  of  two  individuals  are:  length  of  pedicle  valve  22.5  mm.  and 
21  mm.,  length  of  brachial  valve  18  mm.  and  17  mm.,  width  ±38  mm.  and 
31  mm.,  thickness  18  mm.  and  14  mm.,  height  of  cardinal  area  3.5  mm. 
and  3.2  mm. 

Pedicle  valve  more  or  less  strongly  convex,  the  greatest  convexity  pos- 
terior to  the  middle,  the  surface  curving  more  or  less  abruptly  from  the 
umbonal  region  to  the  cardinal  margin  on  each  side  of  the  beak,  more 
gently  to  the  antero-lateral  margins,  compressed  towards  the  cardinal  ex- 
tremities; beak  small,  pointed,  incurved;  cardinal  area  of  moderate 
height,  arched,  the  curvature  increasing  towards  the  beak,  lateral  mar- 
gins sharply  defined,  sloping  from  the  beak  to  the  caixlinal  extremities ; 
lateral  slopes  convex  towards  the  center  of  the  valve,  more  or  less  com- 
pressed towards  the  cardinal  extremities,  each  marked  by  from  18  to  20 
subangular  plications  along  the  antero-lateral  margin  which  originate 
from  10  to  13  plications  starting  at  the  beak  or  along  the  cardinal  mar- 
gin ;  from  3  to  5  of  the  original  plications  on  each  side  of  the  beak  divide 
into  2  or  3  in,  or  a  little  in  front  of,  the  umbonal  region  and  con- 
tinue in  more  or  less  distinct  fascicles  to  the  anterior  margin,  the  fur- 
rows between  these  groups  of  plications  being  stronger  and  deeper  than 
those  between  the  members  of  the  group ;  mesial  sinus  sharply  defined  at 
the  beak,  becoming  less  well  defined  anteriorly,  it  is  subangular  or 
rounded  in  the  bottom,  of  moderate  depth  and  sometimes  somewhat  pro- 
duced anteriorly  into  a  nasute  or  lingual  extension,  it  is  marked  by  a 
median  plication  which  originates  near  the  beak  and  bifurcates  in  passing 
to  the  anterior  margin ;  on  each  side  there  are  from  3  to  5  plications  wdiich 
originate  from  the  inner  margins  of  the  lateral  bounding  plications  or 
through  the  bifurcation  of  such  plications. 

Brachial  valve  equally  or  a  little  less  convex  than  the  pedicle,  the  great- 
est convexity  usually  near  the  middle ;  mesial  sinus  sharply  denned  to- 
wards the  beak  by  a  pair  of  deeper  and  stronger  furrows  than  those  be- 
tween the  other  plications,  becoming  somewhat  less  sharply  defined  ante- 


320  MISSISSIPPI^    BRACHIOPODA 

riorly,  it  is  subangular  or  rounded  in  contour  and  sometimes  becomes 
quite  strongly  elevated  in  front,  marked  by  bifurcating  plications  to  the 
number  of  from  8  to  12  a1  the  anterior  masgin,  all  of  which  originate 
from  a  single  one  al  the  beak;  lateral  slopes  most  convex  in  the  umbonal 
region,  the  curvature  more  abrupt  to  the  cardinal  margin,  compressed 
towards  the  cardinal  extremities,  marked  by  plications  similar  in  form 
and  number  to  tbose  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  usually  more  or  less  com- 
pletely lacking  in  the  specimens,  but  a  few  examples  retain  fine  radiating 
stria'  which  doubtless  originally  covered  the  entire  shell  surface,  and  also 
still  finer  concentric  stria-.  Concentric  lines  of  growth  are  more  or  less 
strongly  marked  ii] some  examples. 

Remarks. — This  species  is  characteristic  of  the  Chouteau  limestone.  It 
may  be  easily  recognized  by  the  more  or  less  distinct  fasciculate  arrange- 
ment of  the  plications,  in  winch  respect  it  is  similar  to  S.  cameratus  of  the 
Pennsylvania)!  faunas.  S.  cameratus,  however,  attains  a  much  larger  size 
and  in  it  the  fasciculate  arrangement  of  the  plications  is  carried  to  a 
greater  extreme. 

Horizon. — Chouteau  limestone. 

Spirifer  biplicatus  Hall 
Plate  XXXIX,  Figs.  24-26 

1858.     Spirifer  biplicatus  Hall,  Geol.  Surv.  Iowa,  vol.  1,  pt.  2,  p.  519,  pi. 

7,  fig.  5b  (not  fig.  5a). 
1900.     Spirifer  biplicatus  "Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10,  p.  77, 

pi.  2,  figs.  6-7. 

Description. — Shell  small,  much  wider  than  long,  subtriangular  in  out- 
line, with  the  apex  of  the  triangle  truncated  at  the  anterior  margin,  car- 
dinal extremities  produced  into  extremely  elongate,  mucronate  points. 
The  dimensions  of  the  internal  cast  of  a  pedicle  valve  are :  length  9  mm., 
width  along  the  hinge-line  50  mm.,  convexity  5  mm.  The  dimensions  of  a 
brachial  valve  are:  length  8.5  mm.,  width  along  the  hinge-line,  estimated, 
42  mm.,  convexity  4  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  umbo  rather  prominent,  the  surface  of  the  valve  com- 
pressed laterally;  beak  small,  incurved;  cardinal  area  narrow,  lateral 
margins  not  sharply  defined  in  the  internal  cast,  the  only  condition  in 
which  the  species  has  been  observed,  but  probably  sharply  defined  in  the 
original  condition ;  lateral  slopes  convex  antero-posteriorly,  the  curvature 
more  abrupt  to  the  cardinal  margin,  compressed  towards  the  cardinal  ex- 
tremities, each  marked  by  about  12  simple,  rounded  plications  which  or- 
iginate along  the  cardinal  margin  and  grow  successively  smaller  towards 
the  cardinal  extremities ;  mesial  sinus  narrow  and  shallow,  bounded  by  a 


spirifer  321 

pair  of  broad  plications  which  are  much  stronger  than  any  others  on  the 
valve,  marked  by  a  single  median  plication  which  originates  in  the  um- 
bonal  region  and  continues  without  division  to  the  anterior  margin. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  the  middle ;  mesial  fold  narrow,  sharply  defined  by  a  pair  of 
furrows  deeper  and  wider  than  those  between  the  plications,  but  little 
elevated  above  the  general  surface  of  the  valve,  divided  by  a  median  fur- 
row originating  in  the  umbonal  region  which  is  weaker  than  those  between 
the  plications;  lateral  slopes  convex  antero-posteriorly,  curving  more  ab- 
ruptly to  the  cardinal  margin,  the  surface  compressed  towards  the  car- 
dinal extremities,  marked  by  plications  similar  in  form  and  number  to 
those  of  the  opposite  valve. 

None  of  the  specimens  observed  are  in  a  proper  condition  of  preserva- 
tion to  show  the  finer  markings  of  the  shell,  although  they  consisted  of 
concentric  lines.  More  or  less  distinct  concentric  lines  of  growth  are 
sometimes  recognizable  upon  the  casts. 

Remarks.— With  his  original  definition  of  the  species  8.  biplicatus,  Hall 
illustrated  two  brachial  valves,  one  of  which  is  from  the  Chonopectus 
sandstone  at  Burlington,  Iowa,  the  other  from  the  higher  yellow  sand- 
stone of  the  Kinderhook  section  at  the  same  locality.1  A  large  number 
of  specimens  have  been  studied  in  connection  with  the  present  investiga- 
tion and  they  seem  clearly  to  be  representatives  of  two  distinct  species. 
The  name  S.  biplicatus  is  restricted  to  the  form  from  the  Chonopectus  sand- 
stone which  seems  to  correspond  more  closely  with  the  definition  of  the 
species,  the  other  form  being  here  named  8.  biplicoides.  The  8.  biplicatus 
is  characterized  by  the  distinctly  biplicate  fold  and  sinus,  while  S.  biplicoides 
has  an  additional  lateral  plication  upon  each  lateral  slope  of  the  fold  and 
sinus  in  the  full  grown  shells.  The  cardinal  extremities  of  S.  biplicatus 
are  also  much  more  extended  into  slender  points  than  in  S.  biplicoides,  the 
length  of  the  extensions,  when  complete,  being  equal  to  one-half  the  dis- 
tance along  the  hinge-line  from  a  point  beneath  the  beak  to  the  extreme 
end  of  the  hinge-line.  The  length  of  the  body  of  the  shell  is  proportion- 
ately less  in  S.  biplicatus  and  the  number  of  plications  as  seen  in  the  caste 
is  usually  smaller,  although  this  last  character  would  perhaps  not  distin- 
guish the  two  forms  if  the  shell  itself  were  preserved. 

H orizon.— Chonopectus   sandstone    of   the   Kinderhook. 

1  The  specimen  from  the  higher  yellow  sandstone  is  erroneously  stated  by  Hall 
to  be  from  the  oolitic  limestone  bed  of  the  Kinderhook  section  at  Burlington,  but 
the  specimen  itself  is  preserved  in  the  American  Museum  of  Natural  History  in 
New  York,  and  is  clearly  from  the  upper  Yellow  sandstone. 


-11 


322  iMISSISSII'I'IAN    BRACHIOPODA 

Si'iuiFi'.R  LOUIS1ANENSIS   Rowley 

I  Male  XL,  Figs.  1-215 

1900.     Spirifi  ;•  Itittisituit  nsis  Rowley,  Am.  Geol.,  vol.  25,  p.  262,  pi.  5,  figs. 
18-20,  64. 

I)(  s< ■ription.  —  Shell  small,  subtriangular  to  subsemicircular  or  subsemi- 
elliptical  in  outline,  wider  than  long,  the  greatest  width  along  the  tinge- 
line,  the  cardinal  extremities  more  or  less  acutely  angular.  The  dimen- 
sions of  two  examples  from  the  type  locality  are:  length  of  pedicle  valve 
11.9  mm.  and  10  mm.,  Length  of  brachial  valve  10.8  mm.  and  8.9  mm.,  width 
along  hinge-line '13.6  mm.  and  13.2  mm.,  thickness  10  mm.  and  8.4  mm., 
height  of  cardinal  area  2.4  mm.  and  2.2  mm.,  width  of  mesial  sinus  in  front 
4  mm.  and  ',)  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle  and  well  hack  on  the  umbonal  region,  the  umbo  prominent  and 
narrow,  the  surface  curving  abruptly  to  the  cardinal  margin  on  each  side 
of  the  beak  and  rather  steeply  to  the  antero-lateral  margins;  beak  small, 
pointed  and  incurved ;  cardinal  area  of  moderate  height,  arched,  the 
curvature  becoming  greater  towards  the  beak,  broadly  triangular  in  out- 
line, its  lateral  margins  sharply  defined,  sloping  from  the  beak  to  the 
cardinal  extremities  with  a  gently  convex  curve  which  becomes  more  ab- 
rupt distally;  lateral  slopes  convex  antero-posteriorly,  the  posterior  slope 
to  the  cardinal  margin  more  abrupt,  the  slope  from  the  umbo  to  the  car- 
dinal extremities  nearly  straight  or  slightly  convex,  each  lateral  slope 
marked  by  10  to  13,  usually  simple,  rounded,  radiating  plications,  the 
first  one  or  two  on  each  side  of  the  sinus  sometimes  bifurcating  close  up 
to  the  beak;  mesial  sinus  narrow,  shallow,  rounded  in  the  bottom,  sharply 
defined  by  angular  plications  at  the  beak,  sometimes  losing  more  or  less 
of  its  definition  anteriorly,  marked  by  a  median  plication  which  originates 
near  the  beak  and  continues  without  division  to  the  anterior  margin,  on 
each  side  are  one,  or  more  rarely  two,plications  which  originate  from  the 
inner  margin  of  the  bounding  plications. 

Brachial  valve  less  convex  than  the  pedicle,  with  a  narrow,  linear  car- 
dinal area ;  mesial  fold  scarcely  elevated  above  the  general  surface  of  the 
valve  except  towards  the  front,  bounded  by  a  pair  of  furrows  which  are 
broader  and  deeper  than  the  other  furrows  of  the  valve,  marked  by  from 
2  to  5  plications,  all  of  which  originate  from  a  single  one  at  the  beak ; 
lateral  slopes  most  convex  towards  the  mesial  fold,  the  surface  curving 
more  abruptly  to  the  cardinal  margin,  becoming  more  or  less  compressed 
towards  the  cardinal  extremities,  marked  by  plications  similar  in  form  and 
number  to  those  of  the  opposite  valve. 

Surface  of  shell,  when  well  preserved,  marked  by  exceedingly  fine,  reg- 
ular, concentric  striae,  about  15  of  which  occupy  the  space  of  1  mm.  and 


SI  IK  IF  I  K  323 

by  slightly  coarser  radiating  striae  which  are  more  conspicuous  in  the 
furrows  between  the  plications  than  upon  the  plications  themselves. 
-  IU  marks. — This  species  may  be  easily  recognized  by  its  deep  pedicle 
valve,  its  narrow  umbonal  region,  and  narrow  fold  and  sinus.  The  minute 
surface  markings  have  been  observed  only  upon  specimens  from  the  white 
cherts  at  Louisiana,  Missouri. 

Horizon. — Upper  Kinderhook  and  lower  Burlington  limestone. 

Spirifer  biplicoides  n.  sp. 

Plate  XXXIX,  Figs.  27-30 
1858.     Spirifer  biplicatus  Hall.  Geol.  Surv.  Iowa,  vol.  1,  pt.  2.  p.  519,  pi.  7, 

fig.  5a  (not  fig.  5b). 
1901.     Spirifer  centronatus  Weller,  Trans.  St.  Louis  Acad.  Sci..   vol.  11, 

p.  163,  pi.  14,  figs.  3-4. 

Description. — Shell  small,  much  broader  than  long,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  acuminate.  The  dimensions 
of  a  pedicle  valve  are:  length  11  mm.,  width  along  the  hinge-line  32  mm., 
convexity  5.5  mm.  The  dimensions  of  a  brachial  valve  are:  length  8  mm., 
width  along  the  hinge-line  25  mm.,  convexity  3.5  mm. 

Pedicle  valve  strongly  convex  from  beak  to  front,  the  greatest  convex- 
ity near  or  posterior  to  the  middle  of  the  shell,  the  surface  compressed 
towards  the  cardinal  extremities  which  are  produced  into  more  or  less 
elongate,  attenuate  points;  beak  small,  pointed,  incurved;  cardinal  area 
narrow,  arched,  the  lateral  margins  sharply  defined,  sloping  from  the 
beak  to  the  cardinal  extremities ;  lateral  slopes  convex  antero-posteriorly, 
becoming  compressed  distally,  each  marked  by  from  12  to  16  simple, 
rounded  plications;  mesial  sinus  narrow  and  shallow,  defined  to  the  beak, 
the  bounding  plications  much  broader  than  any  of  the  plications  of  the 
lateral  slopes,  marked  by  a  low  and  narrow  median  plication  which  orig- 
inates in  the  umbonal  region  and  continues  without  division  to  the  ante- 
rior margin,  a  little  in  front  of  the  point  of  origin  of  the  median  plication 
each  of  the  broad,  bounding  plications  is  divided  by  a  narrow  groove  much 
weaker  than  those  between  the  plications  of  the  lateral  slopes,  the  inner 
division  of  the  plication  occupying  the  lateral  slopes  of  the  sinus. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
or  posterior  to  the  middle,  compressed  towards  the  cardinal  extremities; 
mesial  sinus  sharply  defined  by  a  pair  of  furrows  which  are  distinctly 
broader  and  stronger  than  those  between  the  other  plications,  it  is  de- 
pressed and  not  elevated  above  the  general  surface  of  the  valve  posteriorly 
and  is  but  slightly  elevated  anteriorly,  it  is  simple  at  the  beak,  is  divided 
by  a  median  furrow  in  the  umbonal  region  and  further  towards  the  front, 
in  mature  shells  each  of  the  lateral  divisions  is  again  subdivided,  all  the 
furrows  of  the  fold  being  weaker  than  those  which  separate  the  plications 


:„'l  MISSISSIPPIAN    BRACHIOPODA 

upon  the  Lateral  slopes  of  the  shell;  Lateral  slopes  of  the  valve  depressed 
convex,  marked  by  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve. 

The  liner  surface  markings  of  the  shell  have  only  been  observed  upon 
squeezes  taken  from  natural  moulds  which  do  not  perfectly  preserve  their 
character.  They  consist,  so  far  as  can  be  seen,  of  fine,  concentric,  sub- 
lamellose  lines  of  growth  which  are  more  or  less  crowded  at  intervals, 
especially  towards  the  front  of  the  shell. 

Remarks. — This  species  has  only  been  observed  -in  the  condition  of  de- 
tached and  more  or  less  incomplete  separate  valves,  and  in  this  condition 
it  is  not  always  easy  to  distinguish  between  it  and  S.  platynotus,  with  which 
it  is  sometimes  associated.  It  does  not  attain  so  large  a  size  as 
S.  platynotus,  it  does  not  exhibit  so  greal  variation  in  the  Lateral  extension 
of  the  hinge-line,  being  uniformly  more  extended  than  that  species  and 
with  the  angular  cardinal  extremities  more  acuminate,  the  lateral  bound- 
ing plications  of  the  sinus  of  the  pedicle  valve  are  conspicuously  broader 
and  more  differentiated  from  the  other  plications  of  the  valve,  the  sinus 
itself  is  narrow  and  has  but  one  lateral  plication  on  each  side  which  is 
less  sharply  differentiated  from  the  bounding  plication  than  from  the 
median  one.  The  fold  of  the  brachial  valve  in  the  two  species  is  similar 
in  being  little  or  not  at  all  elevated  above  the  general  surface,  but  it  is 
more  sharply  differentiated  in  S.  biplicoides. 

The  species  differs  from  S.  louisianensis  in  its  proportionately  broader 
shell,  more  extended  cardinal  extremities,  shallower  pedicle  valve  with 
broader  umbonal  region  and  lower  cardinal  area.  The  bounding  plications 
of  the  mesial  sinus  of  the  pedicle  valve  are  also  broader  and  more  differ- 
entiated in  this  species  than  in  S.  leuisianensis. 

Members  of  this  species  were  originally  included  by  Hall  under  his 
species  S.  biplicatus,  indeed,  of  the  two  specimens  figured  as  the  types  of 
that  species,  one  is  an  example  of  S.  biplicoides.  The  distinctions  between 
the  two  species  are  pointed  out  under  the  discussion  of  8.  biplicatus,  but 
besides  being  different  in  character,  the  two  forms  occur  at  different 
geologic  horizons  within  the  Kinderhook. 

Horizon. — Kinderhook. 

Spirifer  insculptus  Rowley 
Plate  XL,  Figs.  30-34 ;  Plate  XLI,  Figs.  1-5 

1900.  Spirifer  insculptus  Rowley,  Am.  Geol.,  vol.  25,  p.  268,  pi.  5,  figs. 
1-3. 
Description. — Shell  above  medium  size,  much  wider  than  long,  the  great- 
est width  along  the  hinge-line,  the  cardinal  extremities  acutely  angular. 
The  dimensions  of  a  nearly  perfect  specimen,  the  holotype,  are:  length  of 
pedicle  valve  24  mm.,  length  of  brachial  valve  20  mm.,  width  along  hinge- 


SPIRIFEK  325 

line  -]— 60  mm.,  thickness  23.5  mm.,  height  of  cardinal  area  11.5  mm.  The 
dimensions  of  another  specimen,  less  extended  along  the  hinge-line  are: 
tfength  of  pedicle  valve  24  mm.,  length  of  brachial  valve  19  mm.,  width 
along  hinge-line  38.5  mm.,  thickness  20  mm.,  height  of  cardinal  area 
10  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the  ura- 
honal  region  to  the  antero-lateral  and  anterior  margins  with  a  very  gently 
convex  curve,  the  slope  becoming  nearly  straight  beyond  the  middle  of 
the  valve,  curving  somewhat  more  abruptly  to  the  cardinal  margin  for  a 
short  distance  on  either  side  of  the  beak,  becoming  slightly  compressed 
subparallel  with  the  cardinal  area  towards  the  cardinal  extremities; 
mesial  sinus  well  defined,  originating  at  the  beak  where  it  is  narrow  and 
shallow,  becoming  rapidly  broader  and  attaining  a  moderate  depth  to- 
wards the  front,  nearly  flat  across  the  bottom  in  front  with  gently  sloping 
sides;  beak  small,  rather  obtusely  pointed,  a  little  incurved;  cardinal 
area  high,  the  inferior  portion  nearly  flat  and  lying  in  an  angle  of  about 
90  degrees  or  a  little  less  to  the  plane  of  the  valve,  the  higher  portion  of 
the  area  concave  with  the  curvature  increasing  to  the  beak,  the  lateral 
margins  sharply  defined  and  sloping  in  nearly  straight  or  slightly  convex 
lines  from  the  beak  to  the  cardinal  extremities.  Surface  of  valve  marked 
by  rounded,  radiating  plications,  which  occupy  both  the  sinus  and  the 
lateral  slopes,  the  larger  of  which  measure  about  2  mm.  from  center  to 
center,  from  12  to  17  are  present  upon  each  lateral  slope,  all  of  which  are 
simple  and  originate  along  the  cardinal  margin,  growing  successively 
smaller  towards  the  cardinal  extremities,  the  plications  of  the  sinus  are 
about  six  in  number,  the  median  one  originates  in  the  umbonal  portion 
of  the  valve  and  continues  to  the  front  margin  without  division,  the  lat- 
eral ones  all  originate  as  offshoots  from  the  inner  sides  of  the  lateral 
bounding  plications  of  the  sinus  and  continue  to  the  front  without  division 
and  essentially  parallel  with  the  median  one. 

Brachial  valve  moderately  convex  with  the  curvature  more  abrupt  to 
the  cardinal  margin,  becoming  a  little  compressed  towards  the  cardinal 
extremities;  mesial  fold  well  defined,  flat  on  top,  sloping  abruptly  to  its 
lateral  margins  on  the  sides  anteriorly,  of  only  moderate  height,  becoming 
rapidly  broader  towards  the  front ;  the  beak  small  and  obtuse,  only 
slightly  protuberant  beyond  the  cardinal  margin,  and  slightly  incurved. 
Surface  marked  by  plications  entirely  similar  to  those  of  the  opposite 
valve  in  form  and  number,  all  those  of  the  fold  originate  through  the  bi- 
furcation of  the  original  simple  plication  at  the  beak  and  then  through 
the  division  of  these  two  main  branches  from  their  inner  margins,  all  the 
plications  continuing  to  the  front  in  a  nearly  parallel  direction. 

Surface  of  both  valves,  in  addition  to  the  plications,  marked  by  very 
regular,  somewhat  crowded,  subimbricating,  concentric  markings,  and  by 
occasional  stronger  lines  of  growth. 


326  mississiitian  BBACHIOPODA 

Remarks. — This  species  may  be  easily  recognized  by  its  higb  cardinal 
area,  its  extended  binge-line,  and  especially  by  its  broad,  flattened  fold 
and  sinus  whose  plications  are  essentially  parallel  with  the  median  line 
of  the  shell. 

Horizon. — Lower  Burlington  limestone. 

Spiriper  eegrandensis  n.  sp. 
Plate  XL,  Figs.  24-29 

Description. — Shell  below  medium  size,  broadly  subtriangular  in  out- 
line, the  width  more  than  twice  the  length,  the  greatest  width  along  the 
hinge-line,  the  cardinal  extremities  acutely  angular.  The  dimensions  of 
»  nearly  perfect  individual  are:  length  of  pedicle  valve  from  beak  to 
front  17.")  mm.,  length  of  brachial  valve  14.5  mm.,  width  along  hinge-line 
36  mm.,  thickness  15.5  mm.,  height  of  cardinal  area  7  mm. 

Pedicle  valve  broadly  subpyramidal  in  form,  the  greatest  depth  nearly 
opposite  the  hinge-line;  beak  small,  sharply  pointed,  moderately  incurved 
over  the  area;  cardinal  area  high,  broadly  subtriangular  in  outline,  the 
inferior  portion  nearly  flat  and  making  an  angle  of  about  90  degrees  to 
the  plane  of  the  valve,  becoming  concave  towards  the  beak,  lateral  mar- 
gins sharply  defined,  sloping  regularly  from  the  beak  nearly  to  the  car- 
dinal extremities  beyond  which  point  the  slope  becomes  more  abrupt,  del- 
thyrium  higher  than  wide ;  lateral  slopes  gently  convex,  the  curvature 
most  abrupt  to  the  cardinal  margin  near  the  beak,  each  marked  by  from 
16  to  18  simple,  subangular  plications  which  become  successively  smaller 
towards  the  cardinal  extremities ;  mesial  sinus  shallow,  sharply  defined 
from  beak  to  front  by  angular  plications,  marked  by  a  median  plication 
which  originates  near  the  beak  and  becomes  strong  and  angular  towards 
the  front,  in  the  larger  individuals  each  side  of  the  sinus  is  marked  by  a 
single  plication  much  weaker  than  the  median  one,  which  originates  from 
the  inner  margins  of  the  lateral  bounding  plications. 

Brachial  valve  much  shallower  than  the  pedicle,  with  a  narrow,  linear 
cardinal  area;  mesial  fold  low,  flattened  on  top,  sharply  defined  to  the 
beak  where  it  is  simple,  in  the  umbonal  region  the  single  plication  is 
divided  into  two  by  a  median  furrow  corresponding  to  the  median  plica- 
tion of  the  opposite  valve,  each  side  being  again  divided  in  the  larger  ex- 
amples between  the  umbo  and  the  front  of  the  shell ;  lateral  slopes  convex 
antero-posteriorly,  the  surface  curving  much  more  abruptly  to  the  cardinal 
margin,  each  marked  by  plications  similar  in  form  and  number  to  those  of 
the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  preserved  in  any  of  the 
specimens  observed,  but  .several  concentric  lines  of  growth  are  present 
which  are  more  crowded  towards  the  front  of  the  shell. 

Remarks.— This  species  has  sometimes  been  identified  as  8.   biplicatus, 


SPIRIFER  327 

an  identification  which  has  doubtless  been  made  because  of  the  strong 
median  plication  of  the  sinus;  the  two  species,  however,  are  totally  differ- 
ent,  S.  legrandensis  having'  a  high  cardinal  area,  while  8.  biplicatus  has  a 
low  one,  and  the  cardinal  extremities  are  never  extended  into  the  ex- 
tremely attenuated  points  in  8.  legrandt  nsis  as  they  are  in  8.  biplicatus. 
There  is  no  species  of  Spirifer  in  any  of  our  Mississippiaa  faunas  which 
can  be  compared  with  this  one.  It  resembles,  however,  S.  macbridei  Calvin, 
from  the  Upper  Devonion  fauna  at  Rockford,  Iowa,  but  it  is  proportionally 
much  broader,  with  a  more  nearly  flat  cardinal  area,  and  has  a  larger  num- 
ber of  plications.  It  also  resembles  8.  bimesialis  Hall,  also  from  the  Upper 
Devonian  of  Iowa,  but  it  attains  a  larger  size  with  a  somewhat  higher 
area  and  more  incurved  beak,  and  in  the  mature  shell  it  often  has  a  pair 
of  lateral  plications  in  the  sinus  in  addition  to  the  strong  median  one. 
Horizon. — Kinderhook. 

Spirifer  subcequalis  Hall 
Plate  XLIII,  Figs.  1-10 

1858.     Spirifer  subequalis  Hall.  Geol.  Iowa.  vol.  1.  pt.  2,  p.  663,  pi.  23, 

figs.  9a-c. 
1883.     Spirifer  subcequalis  Hall,  Rep.  X.  Y.  State  Geol.  for  1882,  pi.  (31) 

56,  figs.  13-14. 

1894.  Spirifer  subcequalis  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pi.  27,  fig.  2. 

1895.  Spirifer  subcequalis  Hall  and  Clarke.  Pal.  N.  Y..  vol.  8,  pt.  2,  pi.  31, 

figs.  13-14. 
1906.     Spirifer  subcequalis  Beede,  30th  Ann.  Rep.   Geol.  Survev  Ind.,  p. 
1316,  pi.  21,  figs.  3-3b. 

Description. — Shell  above  medium  size,  much  wider  than  long,  the  great- 
est width  along  the  hinge-line,  the  cardinal  extremities  acutely  angular. 
The  dimensions  of  a  nearly  perfect  individual  are :  length  of  pedicle  valve 
29.8  mm.,  length  of  brachial  valve  23.5  mm.,  greatest  width,  along  the 
hinge-line  60  mm.,  thickness  23  mm.,  height  of  cardinal  area  5.5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  sloping 
with  a  gently  convex  curvature  from  the  umbonal  region  nearly  to  the 
cardinal  extremities  where  it  becomes  a  little  compressed,  to  the  cardinal 
margin  the  surface  slopes  with  a  short  and  rather  abrupt  curvature,  es- 
pecially near  the  beak,  the  slope  to  the  anterior  and  antero-lateral  mar- 
gins long  and  regularly  curved;  beak  small,  pointed  and  moderately  in- 
curved ;  mesial  sinus  shallow,  rounded  in  the  bottom,  of  moderate  width, 
ill-defined  laterally;  cardinal  area  concave,  becoming  more  curved  to- 
wards the  beak,  the  lower  and  more  flattened  portion  lying  at  an  angle  of 
about  65  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply 
defined  and  sloping  with  a  gently  convex  curvature  from  the  beak  to  the 
cardinal  extremities,  the  surface  marked  by  vertical  stria'.     Surface  of 


:!2S  MISSISSIPPI  AN    BRACHIOPODA 

the  valve  marked  by  about  7")  or  80  flattened,  radiating  plications  al  the 
margin,  those  in  the  central  portion  of  the  valve,  in  the  sinus  and  for 
some  distance  on  either  side,  increase  by  bifurcation  near  the  beak  or 
more  rarely  between  the  beak  and  the  middle  of  the  valve,  from  16  to  20 
plications  occupying  the  sinus  ill  front  with  about  30  upon  each  lateral 
slope;  rather  fine,  crowded,  subimbricating  concentric  markings  cross  the 
radiating  plications,  usually  being  more  conspicuous  towards  the  front 
margin,  in  addition  to  which  are  occasional  much  stronger  concentric 
lines  of  growth, 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity  near 
the  middle,  the  surface  convex  antero-posteriorly,  but  gently  concave 
from  the  median  region  in  the  long  slope  to  the  cardinal  extremities,  the 
curvature  to  the  cardinal  margin  shorter  and  more  abrupt  than  that  to 
the  anterior  margin  ;  mesial  fold  originating  at  the  beak  where  it  is  rather 
sharply  defined  by  deeper  furrows,  but  scarcely  elevated  above  the  gen- 
eral surface  of  the  valve,  anteriorly  it  is  rounded,  becoming  ill-defined, 
and  is  essentially  undifferentiated  from  the  lateral  slopes  of  the  valve; 
the  beak  incurved,  the  umbonal  region  but  little  protuberant  beyond  the 
cardinal  margin  ;  the  cardinal  area  narrow,  with  sharply  defined  margin. 
Surface  marked  by  radiating  plications  and  concentric  lines  entirely  sim- 
ilar to  those  of  the  opposite  valve. 

Remarks. — This  species  seems  to  be  a  rather  rare  form  and  has  some- 
times been  confused  with  S.  tcnuicostatus.  It  differs  from  that  species 
in  having  rather  coarser  and  much  less  angular  plications,  and  less  con- 
spicuous, sublamellose,  concentric  markings.  The  number  of  plications 
in  the  specimen  mentioned  above  is  fully  equal  to  the  number  usually 
recognized  in  examples  of  S.  tcnuicostatus,  but  it  a  broader  specimen 
than  is  often  found  in  the  other  species  and  consequently  the  plications 
themselves  are  somewhat  wider,  about  8  or  9  in  the  space  of  10  mm.,  in  the 
median  portion  of  the  front  margin,  while  S.  tenuicostatus  usually  has  about 
10  to  12  in  the  same  space.  The  species  has  much  the  form  and  proportions 
of  S.  forbesi,  but  that  species  is  commonly  somewhat  more  extended  along 
the  hinge-line  and  has  coarser  and  less  commonly  bifurcating  plications. 
In  8.  tenuicostatus  the  plications  bifurcate  more  frequently  towards  the 
front. 

Horizon. — Keokuk  limestone  and  Warsaw  formation. 

Spirifer  tenuicostatus  Hall 
Plate  XLII,  Figs.  4-16 

1858.     Spirifer  t<  nuicostatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  662,  pi.  23. 

figs.  8a-c. 
1906.     Spirifer  subcvqualis  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1316, 

pi.  20,  figs.  4-4b. 


SPIRIFER  329 

Description.— Shell  of  medium  size,  wider  than  long,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimensions  of 
a  nearly  complete  specimen,  one  of  the  cotypes,  are:  length  of  pedicle 
valve  27.5  mm.,  length  of  brachial  valve  24.8  mm.,  width  41  mm.,  thickness 
17.5  mm.,  height  of  cardinal  area  5  mm.  The  dimensions  of  another  one 
of  the  cotypes,  a  pedicle  valve,  are :  length  25  mm.,  greatest  width  41  mm., 
height  of  cardinal  area  7  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  sloping 
rather  abruptly  from  the  umbonal  region  to  the  cardinal  margin,  much 
more  gently  to  the  antero-lateral  margins,  somewhat  compressed  towards 
the  cardinal  extremities ;  beak  small,  pointed  and  moderately  incurved ; 
cardinal  area  arched,  becoming  more  curved  towards  the  beak,  its  lateral 
margins  sharply  defined  and  sloping  gently  from  the  beak  to  the  cardinal 
extremities,  the  surface  marked  by  vertical  stria?;  lateral  slopes  of  the 
valve  each  bearing  28  to  34  narrow,  rounded  plications,  some  of  which 
bifurcate ;  mesial  sinus  rounded  in  the  bottom,  originating  at  the  beak 
where  it  is  sharply  defined,  becoming  more  or  less  ill-defined  anteriorly, 
it  is  marked  by  from  10  to  14  plications  similar  to  those  upon  the  lateral 
slopes  of  the  valve,  the  median  plication  originates  near  the  beak  and 
continues  to  the  front  margin  either  as  a  simple  rib  or  bifurcating,  the 
lateral  plications  originate  from  the  inner  margins  of  the  two  bounding 
plications  or  through  the  bifurcation  of  plications  so  originating. 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity  near 
the  middle ;  mesial  fold  originating  at  the  beak,  it  is  narrow  and  scarcely 
elevated  in  the  umbonal  region  but  becomes  moderately  elevated  an- 
teriorly where  it  is  ill-defined  and  rounded  or  subangular  in  contour, 
it  is  marked  by  from  10  to  14  plications  similar  to  those  of  the  opposite 
valve  which  originate  from  a  single  plication  at  the  beak;  lateral  slopes 
moderately  convex  towrards  the  middle  of  the  valve,  somewhat  compressed 
towards  the  cardinal  extremities,  marked  by  plications  similar  in  form 
and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  consist  of  fine,  more  or  less 
irregular,  raised,  concentric  lines.  Both  valves  are  also  marked  by 
numerous,  imbricating,  sublamellose  lines  of  growth,  which  are  crowded 
near  the  front  of  most  shells. 

l!<  marks.  —  This  species  has  frequently  been  identified  as  8.  subaqualis, 
but  a  critical  examination  of  many  individuals,  including  the  cotypes,  has 
shown  that  these  two  species  are  not  synonymous.  S.  tenuicostatus  has 
somewhat  finer  and  more  angular  plications,  and  also  much  more  con- 
spicuous sublamellose  concentric  markings. 

The  species  is  sometimes  associated  with  S.  lateralis,  and  in  a  crushed 
and  imperfect  condition  there  may  be  some  difficulty  in  distinguishing 
between  them,  but  S:  hit<  ralis  has  more  acutely  angular  cardinal  extremities 
with  a  earinate   median    fold,   and   does  not  possess  the  conspicuous  con- 


330  MlssissiPi'iAN    BRACHIOPODA 

centric  lamellose  lines  of  growth  which  are  so  characteristic  of  S.  tcnui- 
casta  I  us. 

Horizon,     Keokuk  limestone,  Warsaw  formation  and  Salem  limestone. 

Sl'lKll'KK    LATERALIS    Hall 
Plate  XLIII,   Figs.   11-15 

1858.     Spirifer  lateralis  Hall,  Geol.  Eowa,  vol.  1,  pt,  2,  p.  661,  pi.  23,  figs. 

7a-c. 
1901.     Spirifer  lateralis  var.  delicatus  Rowley.  Greene's  Cont.  to  Ind.  Pal., 

vol.  1,  p.  68,  pi.  23.  figs.  21-23. 
1906.     Spirifer  lateralis  delicatus  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind, 

p.  1314,  pi.  20,  figs.  3-3a. 

Description. — Shell  of  medium  size,  much  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimen- 
sions of  a  complete  example,  the  holotype  of  the  species,  are:  length 
20.5  mm.,  width  .">!  mm.,  thickness  Hi  mm.,  height  of  cardinal  area  4  mm. 

Pedicle  valve  with  its  greatest  convexity  near  the  middle,  the  umhonal 
region  broad  and  rather  compressed,  the  surface  curving  strongly  from 
the  beak  to  the  anterior  margin  and  very  gently  in  a  lateral  direction, 
becoming  a  little  compressed  towards  the  cardinal  extremities;  beak 
compressed,  obtusely  pointed,  incurved;  cardinal  area  arched,  the  curva- 
ture becoming  greater  towards  the  beak,  the  inferior  portion  directed 
posteriori}'  nearly  in  the  plane  of  the  valve,  the  lateral  margins  very 
sharply  defined,  sloping  with  a  gently  convex  curve  from  the  beak  to  the 
cardinal  extremities;  lateral  slopes  each  marked  by  25  or  more  fine, 
rounded,  simple  plications,  most  of  which  terminate  posteriorly  along  the 
cardinal  margin,  towards  the  cardinal  extremities  the  plications  become 
faint  and  almost  obsolete;  mesial  sinus  originating  in  the  umhonal 
region,  in  the  posterior  half  of  the  valve  it  is  shallow  and  ill-defined, 
anteriorly  it  becomes  deeper  but  is  still  ill-defined,  at  the  anterior  margin 
it  is  produced  in  a  tongue-like  extension,  it  is  marked  by  plications 
which  are  similar  in  size  to  those  upon  the  lateral  slopes  but,  which  in- 
crease by  division  in  passing  from  the  beak  to  the  anterior  margin,  about 
15  being  present  in  front. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  con- 
vexity near  the  front  margin ;  mesial  fold  not  sharply  defined,  strongly 
elevated  and  carinate  posteriorly,  becoming  more  rounded  towards  the 
front,  posteriorly  where  the  fold  is  carinate  along  the  median  line  of  the 
valve,  the  sides  of  the  fold  are  concave  and  curve  gradually  into  the 
lateral  slopes  of  the  valve,  anteriorly  the  sides  become  convex,  the  fold 
is  occupied  by  about  16  rounded  plications  which  originate  through  the 
division  of  probably  a  single  one  at  the  beak ;  lateral  slopes  of  the  valve 


SPIRIFER  331 

strongly  convex  from  the  cardinal  to  the  anterior  margins,  somewhat 
compressed  towards  the  cardinal  extremities,  marked  by  plications 
similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  preserved  on  the 
specimens  observed,  but  several  concentric  lines  of  growth  of  variable 
strength  are  usually  present,  becoming  stronger  and  more  frequent 
towards  the  anterior  margin  in  mature  shells. 

Remarks. — This  species  is  especially  characterized  by  the  strongly  car- 
mate  mesial  fold  of  the  brachial  valve,  and  when  that  portion  of  the 
shell  is  preserved  it  is  always  easy  of  identification.  In  its  surface  char- 
acters, especially  the  size  and  character  of  the  plications,  the  species  re- 
sembles S.  tcnuicostatus,  and  worn,  fragmentary  examples  of  the  two 
i-.pecies  are,  sometimes  indistinguishable.  8.  lateralis,  however,  does  not 
possess  the  bifurcating  plications  nor  the  conspicuous  lamellose,  concentric 
markings  of  S.  tcnuicostatus,  and  the  character  of  the  fold  and  sinus,  as 
well  as  the  general  form  and  proportions  of  the  valves,  are  totally  different 
in  the  two  species,  S.  lateralis  being  proportionally  shorter  with  more 
sharply  angular  cardinal  extremities. 

The  specimen  which  has  been  illustrated  as  S.  lateralis  by  Hall  and  Clarke,1 
is  clearly  not  a  member  of  this  species,  it  has  more  the  aspect  of  an  under- 
sized example  of  S.  logani,  although  the  depth  of  the  sinus  seems  to  be  too 
great  for  an  individual  of  that  species  of  such  a  size.  The  shell  which 
Rowley  has  described  as  8.  lateralis  var.  delicatus  is  scarcely  worthy  of 
varietal  designation,  it  being  only  a  depauperate  individual  in  the  Spergen 
Hill  fauna  of  Indiana,  where  many  species  are  represented  by  specimens 
smaller  than  the  more  usual  form  of  the  same  species  elsewhere. 

Horizon. — Warsaw  formation  and  Salem  limestone. 

Spirifeb  fobbesi  Norwood  and  Pratten 
Plate  XLTI,  Pigs.  1-3;  Plate  XLIII,  Fig.  16;  Plate  LXXXIII,  Figs.  1-2 

1855.     Spirifcr  Forbesii  Norwood  and  Pratten,  Jour.  Acad.  Nat.  Sci.  Phil., 

(2),  vol.  2,  p.  73,  pi.  9,  figs.  3a-c. 
1S58.     Spirifcr  forbesi  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  600,  pi.  13,  fig.  1. 
1894.     Spirifera  forbesi  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  80,  pi.  40,  fig.  3. 
IS!).").     Spirifer  Forbesi  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  37, 

fig.  18. 

Description. — Shell  above  medium  size,  much  wider  than  long,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  acutely  an- 
gular. The  dimensions  of  a  pedicle  valve  of  usual  size  are :  length 
24  mm.,  width  along  the  hinge-line  54  mm.,  height  of  cardinal  area  5  mm., 
depth  10  mm.  The  dimensions  of  a  larger  individual  with  the  valves  in 
articulation  are :  length  of  pedicle  valve  27.3  mm.,  length  of  brachial  valve 

l  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  32,  figs.  1-3.     (1894). 


332  MISSISSEPPIAN  BRACHIOPODA 

24.:!  mm.,  greatesl  width  along  the  binge-line  73  mm.,  thickness  24.5  mm., 
heighl  of  pedicle  c.arctinnl  area  (5.2  nun.,  height  of  brachial  cardinal  area 
2  mm.,  width  of  simis  in  Eronl   12  mm. 

Pedicle  valve  with  its  greatesl  depth  posterior  to  the  middle,  the  sur- 
face curving  rather  abruptly  from  the  umbonal  region  to  the  cardinal 
margin  on  each  side  of  the  beak,  the  slope  to  the  cardinal  extremities 
nearly  straight  or  slightly  concave,  thai  to  the  anterior  margin  gently 
convex,  towards  the  cardinal  extremities  the  surface  is  somewhat  com- 
pressed in  a  direction  subparallel  to  the  cardinal  urea;  mesial  sinus  rather 
narrow  and  more  or  less  well  defined,  originating  at  the  beak,  usually 
shallow  hut  sometimes  of  moderate  depth,  rounded  in  the  bottom ;  the 
beak  small,  pointed,  rather  strongly  incurved  ;  the  cardinal  area  of  mod- 
erate height,  concave  with  the  curvature  increasing  towards  the  beak,  the 
lateral  margins  sharply  defined  and  subparallel  with  the  hinge-line  well 
out  towards  the  cardinal  extremities,  the  inferior  natter  portion  lyiug  at 
an  angle  of  aboul  120  degrees  to  the  plane  of  the  valve;  the  delthyrium 
large,  broader  than  high.  Each  lateral  slope  marked  by  from  25  to  30 
simple,  depressed,  rounded  plications,  separated  by  narrow,  angular  fur- 
rows, originating  at  or  near  the  cardinal  margin,  those  towards  the  car- 
dinal extremities  becoming  very  faint;  the  mesial  sinus  marked  by  a 
median  plication  originating  in  the  umbonal  region  and  by  two  or  three 
lateral  ones  on  each  side  which  originate  from  the  inner  margins  of  the 
bounding  plications. 

Brachial  valve  subequally  or  less  convex  than  the  pedicle,  its  greatest 
depth  posterior  to  the  middle,  the  surface  curving  rather  abruptly  to  the 
cardinal  margin  and  more  gently  to  the  anterior  margin,  from  the  point  of 
greatest  depth  to  the  cardinal  extremities  the  slope  is  gently  concave,  the 
umbo  slightly  protuberant  beyond  the  cardinal  margin ;  the  mesial  fold  is 
sharply  defined,  gently  convex  or  flattened  on  top,  originating  at  the  beak 
and  only  moderately  elevated  above  the  general  surface  of  the  valve ;  a 
distinct  cardinal  area  with  sharply  defined  lateral  margins  subparallel 
with  the  hinge-line  is  present,  it  is  gently  concave  and  lies  nearly  in  the 
plane  of  the  valve;  the  beak  small,  strongly  incurved.  Each  lateral  slope 
marked  by  plications  entirely  similar  in  form  and  number  to  those  of  the 
opposite  valve,  the  plications  of  the  mesial  fold  also  entirely  similar  to 
those  of  the  sinus  and  all  originating  from  the  subdivision  of  the  single 
plication  at  the  point  of  origin. 

Surface  of  both  valves  marked  by  fine,  crowded,  very  regular,  concen- 
tric, lamellose  lines  which  are  more  closely  crowded  at  intervals  to  form 
more  or  less  conspicuous  lines  of  growth. 

Bemarks. — This  species  is  one  of  the  less  common  Spirifers  in  the  fauna 
of  the  Burlington  limestone,  the  brachial  valve  especially  being  rare.  It 
may  be  easily  recognized  by  its  elongate  hinge-line  and  acute  cardinal  ex- 
tremities.    It  differs  from  the  associated  S.  incertus,  which  has  similar 


SPIRIPER  333 

surface  markings,  in  its  greater  width  and  more  acute  cardinal  extremi- 
ties. Of  the  specimens  figured,  the  smaller  pedicle  valve  is  the  more  typi- 
cal. The  larger  specimen  with  the  valves  in  articulation  has  a  much 
deeper  mesial  sinus  than  is  usual,  but  in  all  other  respects  it  is  in  full 
agreement  Avith  other  representatives  of  the  species. 
Horizon. — Burlington  limestone. 

Spirifer  mundulus  Rowley 
Plate  XLIV,  Figs.  15-19 

1893.  Spirifera  mundula  Rowley,  Am.  Geol.,  vol.  12,  p.  307,  pi.  14,  figs. 
10-12. 

Description. — Shell  small,  very  short  and  broad,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  acutely  pointed.  The  di- 
mensions of  a  nearly  perfect  specimen  are:  length  of  pedicle  valve  8  mm., 
length  of  brachial  valve  6.2  mm.,  width  along  hinge-line  20.5  mm.,  thick- 
ness 7.3  mm.,  height  of  cardinal  area  1.5  mm. 

Pedicle  valve  prominent  in  the  umbonal  region,  the  surface  curving 
abruptly  to  the  cardinal  margin  on  either  side  of  the  beak,  convex  from 
the  cardinal  to  the  antero-lateral  margins  and  sloping  with  a  gently  con- 
cave curvature  laterally  from  the  umbonal  region  to  the  cardinal  extremi- 
ties; mesial  sinus  originating  at  the  beak  where  it  is  a  mere  groove,  con- 
tinuing to  the  front  as  a  rather  narrow  and  shallow  depression,  rounded  in 
the  bottom;  beak  prominent,  pointed,  and  rather  strongly  incurved;  car- 
dinal area  of  only  moderate  height,  concave,  the  lateral  margins  sharply 
defined  and  subparallel  with  the  hinge-line  for  the  greater  portion  of  their 
length.  Surface  of  the  valve  marked  by  simple,  low,  rounded  plications 
which  originate  along  the  cardinal  margin  and  are  confined  to  the  lateral 
.slopes,  from  seven  to  ten  occupy  each  lateral  slope,  of  which  those  bound- 
ing the  sinus  are  much  the  larger. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  convex- 
ity slightly  posterior  to  the  middle,  the  curvature  from  the  beak  to  the 
front  along  the  median  line  nearly  semicircidar.  the  surface  sloping  from 
the  point  of  greatest  convexity  to  the  cardinal  extremities  with  a  gently 
concave  curvature,  rather  strongly  convex  from  the  cardinal  margin  to 
the  antero-lateral  margins ;  mesial  fold  well-defined  to  the  beak,  rather 
narrow  and  only  a  little  elevated  above  the  general  convexity  of  the  valve, 
rounded  on  top  with  a  very  slight  longitudinal  median  groove ;  beak  small, 
obtuse,  scarcely  projecting  beyond  the  cardinal  margin.  Surface  marked 
by  simple,  radiating  plications  entirely  similar  to  those  of  the  opposite 
valve. 

Surface  of  both  valves  marked  by  rather  faint,  concentric  lines  of 
growth  which  are  somewhat  crowded  towards  the  front  margin. 

Remarks. — The  general  aspect  of  this  little  shell  is  more  that  of  a 
Spiriferina  than  a  Spirifer,  but  the  shell  shows  no  indications  of  having 


334 


MISSISSII'I'IAX     HKACIIIOI'OPA 


been  punctate,  and  il  is  not  known  to  possess  a  median  septum  internally 
in  the  pedicle  valve.  Neither  does  il  possess  the  strong,  concentric, 
lamellose  markings  of  the  aon-punctate  Delthyris.  Under  these  circum- 
stances, then,  the  species  may  be  allowed  to  remain  in  the  genus  Spirifer 
to  which  it  was  originally  referred. 
Horizon.- — Lower  Burlington  limestone. 


Spiripeb  imbrex  Hall 

Plate  XLIII,  Kis'.  17 
1858.     Spirifer  imbrex  Hall,  Geol.  Iowa.  vol.  1,  pt.  2,  p.  601,  pi.  13,  fig.  2. 
1883.     Spirifera  imbrex  Hall,  Rep.  X.  Y.  State  Geol.  for  1882,  pi.  (31)  56, 

figs.  11-12. 
1894.    Spirifer  imbrex  Hall  and  Clarke,  Int.  Study  of  Brach.,  pt.  2,  pi.  27, 

fig.  1. 

1894.  Spirifi  ra  imbrex  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  80. 

1895.  Spirifer  imbrex   Hall  and   Clarke,   Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  31, 

figs.  11-12. 

Description. — Shell  above  medium  size,  much  broader  than  long,  the 
greatest  width  along  the  hinge-line.  The  dimensions  of  the  holotype,  a 
brachial  valve,  are:    length  27  mm.,  greatest  width  52  mm.,  depth  7  mm. 

Brachial  valve  moderately  convex,  emarginate  anteriorly  in  the  holo- 
type, greatest  depth  near  the  middle,  the  surface  curving  abruptly  to  the 
cardinal  margin  on  either  side  of  the  beak,  becoming  compressed  towards 
the  cardinal  extremities,  with  a  gently  convex  curvature  to  the  antero- 
lateral margins  ;  mesial  fold  sharply  defined  to  the  beak  where  it  is  narrow, 
gently  convex  and  scarcely  elevated  above  the  lateral  slopes,  becoming 
more  angular  anteriorly  but  only  moderately  elevated;  beak  small, 
incurved.  Surface  of  the  valve  marked  by  from  22  to  24  angular 
plications  upon  each  lateral  slope,  and  about  15  upon  the  mesial 
fold,  the  larger  plications  measuring  about  2  mm.  from  center  to 
center  at  the  front  of  the  shell,  the  plications  of  the  lateral  slopes  fre- 
quently bifurcate  once  in  passing  from  the  cardinal  margin  to  the  front, 
all  those  of  the  fold  originating  from  the  subdivision  of  a  single  one  at 
the  beak.  Crossing  the  plications,  in  the  holotype,  are  two  very  strong 
concentric  lines  of  growth  anterior  to  the  middle  of  the  valve,  and  the 
entire  surface  is  covered  by  fine  concentric,  sublamellose  markings,  about 
three  of  which  occupy  the  space  of  1  mm.,  and  which  are  much  more  con- 
spicuous anteriorly. 

Remarks.- — This  species  seems  to  be  a  rather  unusual  one  in  the  Burliiig- 
ton  limestone  fauna,  the  specimens  which  have  usually  been  so  identified 
being  examples  of  S.  incertus.  Good  examples  of  the  pedicle  valve  of  the 
species  have  not  been  observed,  in  fact  the  holotype,  which  is  a  detached 
brachial  valve,  is  the  only  really  good  example  which  has  been  studied. 
S.  imbrex  and  S.  incertus  are  similar  in  size  and  form,  but  S.  imbrex  is 


SI'IKIFER  335 

characterized  by  its  notably  coarser  and  more  angular  plications.  In  the 
form  of  its  plications  and  the  finer  concentric  markings,  S.  imbrex  resem- 
bles S.  vernonensis, the  larger  and  more  transverse  examples  of  S. vernonensis 
especially  being  suggestive  of  this  species,  but  8.  vernonensis  has  a  more 
elevated  mesial  fold  anteriorly  than  S.  imbrex,  and  the  mesial  sinus  is 
probably  much  deeper,  the  plications  also  are  somewhat  coarser. 
Horizon. — Burlington  limestone. 

Spirifer  incertus  Hall 

Plate  XLI,  Figs.  6-14 

1S58.     Spirifer  incertus  Hall,  Geol.  Iowa,  vol.  1.  pt.  2,  p.  602,  pi.  13,  fig.  3. 

Description.— Shell  of  medium  size,  about  twice  as  wide  as  long,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  angular.  The 
dimensions  of  two  pedicle  valves  are :  length  36  mm.  and  28.5  mm., 
width  65  mm.  and  55  mm.,  convexity  12  mm  and  11  mm.,  height  of  cardinal 
area  5  mm.  and  4  mm.  The  dimensions  of  a  nearly  complete  specimen 
are:  length  of  pedicle  valve  31.5  mm.,  length  of  brachial  valve  29  mm., 
width  along  hinge-line  56  mm.,  thickness  22.5  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  umbonal  region  broad,  the  surface  sloping  rather  gently 
to  the  margins  except  to  the  cardinal  margin  for  a  short  distance  on  each 
side  of  the  beak ;  beak  small,  pointed,  strongly  incurved ;  cardinal  area 
rather  narrow,  strongly  arched,  the  superior  portion  from  the  beak  well 
out  towards  the  cardinal  extremities  being  more  strongly  and  abruptly 
curved,  the  inferior  portion  in  adult  examples  directed  at  an  angle  of  about 
(J0  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply  denned, 
subparallel  with  the  cardinal  margins  through  a  greater  part  of  the  length, 
sloping  abruptly  to  the  cardinal  extremities  distally,  delthyrium  large, 
broadly  triangular;  lateral  slopes  of  the  valve  convex  towards  the  median 
part  of  the  valve,  somewhat  compressed  towards  the  cardinal  extremities, 
each  bearing  about  25  subangular  or  rounded  plications  at  the  margin, 
which  originate  through  bifurcation  from  a  much  smaller  number  at  the 
beak,  the  bifurcations  mostly  taking  place  in  the  umbonal  region,  only 
occasionally  in  the  middle  or  anterior  portion  of  the  shell ;  mesial  sinus 
narrow,  simple  and  sharply  defined  at  the  beak,  becoming  ill-defined  an- 
teriorly where  it  is  rather  broad  and  of  moderate  depth,  rounded  or  sub- 
angular  in  the  bottom,  marked  by  a  median  plication  which  originates 
near  the  beak  and  continues  to  the  front  margin  without  division,  with  4 
or  sometimes  5  plications  on  each  side  which  originate  from  the  inner  mar- 
gin of  the  lateral  bounding  plication  or  through  the  bifurcation  of  plica- 
tions originating  in  that  manner,  all  the  plications  of  the  sinus  are  similar 
in  form  and  size  to  those  of  the  lateral  slopes. 


336  MISSISSIPPIAN   BRACHIOPODA 

Brachial  valve  aboul  as  convex  as  the  pedicle,  the  greatest  convexity 
near  the  middle;  the  lateral  slopes  convex  towards  the  middle  part  of  the 
valve,  the  mosl  abrupt  curvature  being  towards  the  cardinal  margin,  be- 
coming somewhal  compressed  towards  the  cardinal  extremities,  marked  by 
plications  similar  in  form  and  number  to  those  of  the  opposite  valve; 
mesial  fold  defined  by  somewhal  stronger  furrows  posteriorly  but  scarcely 
elevated  above  the  general  surface  of  the  valve,  anteriorly  it  becomes 
moderately  elevated  and  is  rounded  or  subangular  along  the  median  line 
and  ill-defined  laterally,  it  is  marked  by  plications  which  are  similar  in 
form  and  number  to  those  of  the  sinus  of  the  opposite  valve,  all  of  which 
originate  from  a  single  plication  at  the  beak. 

The  surface  of  both  valves  is  marked  by  moderately  fine,  concentric, 
sublamellose  lines  which  arch  posteriorly  as  they  cross  the  plications,  and 
also  by  a  lew  much  stronger  lines  of  growth  which  are  usually  stronger 
and  more   frequent  towards  the  anterior  margin. 

Internally,  as  shown  by  casts  of  the  interior  preserved  in  chert,  the  den- 
tal Lamellae  of  the  pedicle  valve  are  short  and  diverge  at  an  angle  of  about 
60  degrees,  the  muscular  impressions  occupy  a  subovate  area  and  are 
moderately  impressed. 

Eemarks. — This  is  a  rather  common  species  in  the  fauna  of  the  Bur- 
lington limestone  which  has  commonly  been  confused  with  8.  intbrcx. 
The  reason  for  this  confusion  is  doubtless  to  be  found  in  the  imperfect 
specimen  which  was  used  by  Hall  as  the  type  of  the  species,  and  the  single 
unsatisfactory  figure  which  accompanies  the  original  definition.  This 
type  specimen  is  illustrated  herewith,  in  three  views,  and,  in  addition, 
figures  of  more  complete  examples  are  given.  The  species  differs  from 
S.  imbrex  in  having  much  finer  and  less  angular  plications. 

Horizon. — Burlington  limestone. 

Spiriper  carinatus  Rowley 

Plate  XLVI,  Figs.  13-17 

1900.     Spirifer  carinatus  Rowley.  Am.  Geol.,  vol.  25,  p.  269,  pi.  5,  figs.  4-6. 

Description.— Shell  above  medium  size,  wider  than  long,  the  hinge-line 
equaling  or  nearly  equaling  the  greatest  width,  the  cardinal  extremities 
subrectangular.  The  dimensions  of  a  nearly  complete  specimen  with  the 
brachial  valve  somewhat  crushed,  are:  length  of  pedicle  valve  34.5  mm., 
length  of  brachial  valve  29  mm.,  greatest  width  51.5  mm.,  thickness  23.5 
mm.,  height  of  cardinal  area  6  mm. 

Pedicle  valve  with  its  greatest  convexity  near  or  posterior  to  the 
middle,  the  fullness  of  the  valve  extending  well  out  towards  the  lateral 
margins,  the  surface  curving  abruptly  to  the  cardinal  margin  on  either 
side  of  the  beak  and  a  little  more  gently  to  the  anterior  margin,  from 
the  central  portion  of  the  valve  to  the  lateral  margins  the  curvature  is  at 


SPIKIPER  337 

first  gently  convex,  but  as  it  approaches  the  margins  it  becomes  more 
curved  and  drops  to  the  margin  rather  abruptly;  mesial  sinus  originating 
at  the  beak  where  it  is  a  slight,  but  well-defined  groove,  becoming  less 
well-defined  anteriorly,  growing  rapidly  broader  and  deeper  towards  the 
front  where  it  is  very  deep  and  subangular  in  the  bottom,  and  is  pro- 
duced in  a  pointed  lingual  extension;  the  beak  small,  pointed,  rather 
strongly  incurved  ;  the  cardinal  area  of  moderate  height,  the  nearly  flat  or 
gently  concave  inferior  portion  sloping  posteriorly  at  an  angle  of  about 
130  degrees  to  the  plane  of  the  valve,  the  higher  portion  more  concave 
beneath  the  beak,  the  lateral  margins  sharply  defined,  sloping  from  the 
beak  to  the  cardinal  extremities  in  nearly  straight  lines  most  of  the  dis- 
tance, becoming  convexly  curved  distally,  the  delthyrium  of  moderate 
size,  broader  than  long.  Surface  of  the  valve  marked  by  rounded,  bifur- 
cating plications  which  occupy  both  the  lateral  slopes  and  the  sinus,  about 
16  or  18  originate  along  the  cardinal  margin  each  side  of  the  beak,  about 
the  first  ten  of  which  bifurcate  before  reaching  the  middle  of  the  valve, 
so  that  from  26  to  28  are  present  upon  each  lateral  slope  at  the  margin  of 
the  valve,  in  the  sinus  a  median  plication  originates  in  the  umbonal  region 
and  continues  to  the  front  margin  with  one  bifurcation  near  the  middle 
of  the  valve,  the  lateral  plications  of  the  sinus  originate  from  the  inner 
margins  of  the  bounding  plications  or  from  the  bifurcation  of  such 
plications,  from  12  to  15  being  present  at  the  front  margin. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  depth  at  the 
anterior  margin,  the  surface  curving  rather  abruptly  to  the  cardinal  mar- 
gin on  each  side  of  the  beak,  curving  more  gently  to  the  antero-latera] 
margins,  compressed  towards  the  cardinal  extremities;  the  mesial  fold 
defined  to  the  beak,  scarcely  elevated  above  the  general  surface  in  the 
umbonal  region,  but  becoming  very  greatly  elevated  in  front  where  it 
becomes  subcarinate  along  the  median  line,  its  lateral  surfaces  curving 
into  the  lateral  slopes  of  the  valve  with  only  slight  differentiation ;  beak 
small,  incurved.  Surface  marked  by  bifurcating  plications  entirely 
similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  surface  of  both  valves  marked  by  fine,  regular,  sublamellose,  con- 
centric markings,  about  three  of  which  occupy  the  space  of  1  mm.,  and 
by  more-  conspicuous  concentric  lines  of  growth  which  become  more  fre- 
quent and  more  or  less  crowded  anteriorly. 

Remark*. — This  species  is  a  peculiar  one  and  may  be  easily  recognized 
by  the  extension  of  the  convex  fullness  of  the  pedicle  valve  well  out 
towards  the  cardinal  extremities,  in  association  with  a  compression  of  the 
brachial  valve  in  the  same  direction.  The  strong  elevation  of  the  sub- 
carinate fold  of  the  brachial  valve  is  another  notable  character  of  the 
species,  as  is  also  the  character  of  the  bifurcating  plications  of  the  shell. 
The  species  is  perhaps  most  closely  allied  to  S.  incertus,  which  it  resembles 


338 


.MISSISSII'I'IAN    BRACHIOPODA 


in  the  fine,  surface  markings  of  the  shell,  but  the  less  acutely  angular, 
cardinal  extremities,  and  the  peculiar  contour  of    the    shell,  indicated 
above,  afford  sufficienl  means  of  differentiating  the  two  species. 
Horizon. — Lower  Burlington  limestone. 


SPIRIFEB  CRAWFORDSV1IJUBNSIS  H.  Sp. 

Plate  XLVII,  Figs.  1-5 

Description. — Shell  of  medium  size,  much  wider  than  long,  the  greatest 
width  along  the  binge-line,  the  cardinal  extremities  acutely  angular.  The 
dimensions  of  a  nearly  complete  example,  the  bolotype  of  the  specie's, 
are:  length  23  mm.,  width  47  mm.,  thickness  13  mm.,  height  of  cardinal 
area  :5  mm. 

Pedicle  valve  only  moderately  convex  in  the  central  portion,  becoming 
compressed  towards  the  cardinal  extremities,  the  umbonal  region  rather 
broad,  the  surface  sloping  abruptly  from  it  to  the  cardinal  margin  for  a 
short  distance  on  each  side  of  the  beak,  in  other  directions  the  slope  is 
gentle;  beak  small,  acuminate,  pointed  and  incurved;  cardinal  area  rather 
narrow,  arched,  the  curvature  becoming  greater  towards  the  beak,  the 
lateral  margins  sharply  defined,  subparallel  with  the  cardinal  margin 
for  some  distance  on  each  side  of  the  beak,  sloping  to  the  cardinal  ex- 
tremities distally,  surface  of  the  area  marked  with  vertical  stria;  and  by 
longitudinal  lines  of  growth;  the  lateral  slopes  of  the  valve  each  bearing 
12  to  14  simple,  rounded  plications  which  grow  successively  smaller 
towards  the  cardinal  extremities ;  mesial  sinus  originating  at  the  beak, 
rounded  in  the  bottom,  becoming  less  well  defined  anteriorly,  marked  by 
plications  similar  to  those  on  the  lateral  slopes  of  the  valve  except  that 
they  are  somewhat  smaller  than  those  immediately  adjacent  to  the  sinus 
on  each  side ;  they  consist  of  a  median,  simple  one  which  probably  orig- 
inates near  the  beak,  and  of  one  or  two  lateral  ones  on  each  side  which 
originate  from  the  inner  margins  of  the  lateral  bounding  plications. 

Brachial  valve  about  equally  convex  with  the  pedicle,  its  greatest  con- 
vexity near  the  middle;  mesial  fold  originating  at  the  beak,  it  is  scarcely 
elevated  above  the  general  surface  in  the  umbonal  region,  but  becomes 
moderately  elevated  anteriorly  where  it  is  rounded  in  contour,  it  is 
marked  by  about  6  plications  which  are  similar  in  size  and  form  to  those 
of  the  sinus  of  the  opposite  valve,  all  of  which  originate  from  a  single 
plication  at  the  beak;  lateral  slopes  moderately  convex,  compressed 
towards  the  cardinal  extremities,  marked  by  plications  which  are  similar 
in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  consist  of  fine,  crowded,  concentric, 
lamellose  Hues.  At  intervals  they  are  more  closely  crowded  and  give  rise 
to  more  conspicuous  lines  of  growth. 


SPIRIFEK  339 

Remarks. — This  species  is  a  close  ally  of  S.  forbesi  from  the  Burlington 
limestone.  In  general  form,  proportions  and  size  the  two  species  are  essen- 
tially alike,  but  S.  crawfordsvillensis  is  characterized  by  its  coarser  and 
less  numerous  plications  upon  the  lateral  slopes  of  the  shell,  these  being 
only  12  or  14  in  number,  while  in  S.  forbesi  they  exceed  L'O. 

Horizon.—  Keokuk   (Crawfordsville  beds  of  Indiana). 

Sl'IKIPER  WASHINGTONENSIS  n.   sp. 

Plate  XL1V,  Figs.  1-14 

Description. — Shell  of  medium  size,  much  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimen- 
sions of  a  nearly  complete  individual  are:  length  of  pedicle  valve  26.5  mm., 
length  of  brachial  valve  20.5  mm.,  width  41  mm.,  thickness  17.5  mm., 
height  of  cardinal  area  5.5  mm. 

Pedicle  valve  moderately  convex,  the  convexity  reaching  to  the  car- 
dinal extremities  or  with  the  surface  compressed  distally.  the  umbonal 
region  broad,  the  surface  sloping  abruptly  to  the  cardinal  margin  and 
more  gently  to  the  antero-lateral  margin;  beak  small,  pointed,  a  little  in- 
curved; cardinal  area  of  moderate  height,  nearly  flat  except  just  under 
the  beak  where  it  is  arched,  the  inferior  flattened  portion  extends  poste- 
riorly nearly  in  the  plane  of  the  valve,  the  lateral  margins  are  sharply 
angular  and  slope  with  a  gentle  convex  curve  or  in  a  straight  line  from 
the  beak  to  the  cardinal  extremities ;  lateral  slopes  of  the  valve  each 
I  (earing  about  15  simple,  rounded  plications  which  grow  successively 
smaller  towards  the  cardinal  extremities,  the  last  2  or  3  sometimes  becom- 
ing very  faint  or  obsolete:  mesial  sinus  well  defined  at  the  beak,  becom- 
ing broader  and  less  well  defined  anteriorly,  it  is  shallow  or  of  moderate 
depth  and  is  rounded  in  the  bottom,  a  median  plication  originates  near 
the  beak  and  continues  without  division  to  the  anterior  margin  where  it 
is  broad  and  strong,  on  each  side  is  a  single  lateral  plication  which  does 
not  attain  the  strength  of  the  median  one,  originating  from  the  inner  mar- 
gins of  the  bounding  plications. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  mesial  fold  originating  at  the  beak  where  it  is 
bounded  by  furrows  somewhat  deeper  than  those  between  the  plications, 
scarcely  or  not  at  all  elevated  above  the  general  surface  in  the  umbonal 
region,  becoming  moderately  elevated  in  front,  it  is  divided  by  a  rather 
deep  median  groove  corresponding  with  the  median  plication  of  the  oppo- 
site valve,  each  lateral  slope  divided  into  two  plications,  all  four  of  which 
join  in  a  single  plication  at  the  beak;  lateral  slopes  convex  towards  the 
middle  of  the  valve,  becoming  somewhat  compressed  towards  the  cardinal 
extremities,  marked  by  plications  which  are  similar  in  form  and  number 
to  those  of  the  opposite  valve. 


340 


MISSISSIPPI  AN    BRACHIOPODA 


The  minute  surface  markings  of  all  the  specimens  observed  are  nearly 
obliterated  by  the  silicification  of  the  shell,  but  at  a  few  points  very  fine 
Longitudinal  striae  are  preserved.  H  is  not  passible  to  determine  whether 
or  noi  the  surface  is  also  covered  with  fine,  concentric  markings  of  any 
sort.     A  few  concentric  lines  of  growth  are  present. 

Remarks.  This  species  is  quite  distinct  from  any  other  members  of  the 
genus  Sp-irif cr  in  our  Mississippian  faunas.  In  its  minute  surface  markings 
it  seems  to  be  like  the  large  S.  grime'si  and  8.  logcmi,  though  this  cannot  be 
stated  with  certainty  because  of  the  poor  preservation  of  these  characters. 
In  its  general  form  the  species  is  perhaps  more  nearly  like  some  examples 
of  S.  increbescens  than  any  other,  but  the  valves  are  much  less  convex,  the 
cardinal  area  is  flatter  and  lies  in  a  very  different  plane,  and  the  strong 
median  plication  of  the  sinus  is  a  characteristic  feature. 

Horizon. —  Upper  Keokuk   limestone. 

Spikipkk  PELLAENSIS  n.  sp. 
Plate  XLV,  Figs.  1-31 

1858.    Spirifer  keokuk  var.  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  676,  pi.  24, 

figs.  4a-d. 
1883.     Spirifer  keokuk  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.  (30)  55. 

figs.  23-24  (not  figs.  21-22). 
1891.     Spirifer  EocJeymontana?  Whitfield.  Ann.  N.  Y.  Acad.  Sci.,  vol.  5,  p. 

584,  pi.  13,  fig.  20. 
1895.     Spirifera  Rockymontana?  Whitfield,  Geol.  Surv.  Ohio,  vol.  7,  p.  471, 

pi.  9,  fig.  20. 
1895.     Spirifer  Keokuk  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  30, 

figs.  23-24  (not  figs.  21-22). 
1897.     Spirifer  keokuk  AVeller,  Trans.  N.  Y.  Acad.  Sci.,  vol.  16,  p.  257,  pi. 

18,  figs.  10-12. 
1911.     Spirifer  keokuk  Morse,  Proc.  Ohio  Acad.  Sci.,  vol.  5,  p.  377,  fig.  11. 

Description. — Shell  below  medium  size,  usually  wider  than  long,  hut 
occasionally  with  the  length  and  breadth  nearly  equal,  greatest  width  at 
or  in  front  of  the  hinge-line,  the  cardinal  extremities  rounded,  rectangu- 
lar, or  more  or  less  attenuate.  The  dimensions  of  a  full  grown  example 
are :  length  20.5  mm.,  greatest  width  along  the  hinge-line  26.5  mm.,  thick- 
ness 14.8  mm.  The  dimensions  of  another  smaller  and  rounder  example 
are:,  length  15  mm.,  greatest  width  near  the  middle  of  the  shell  17  mm., 
length  of  hinge-line  13  mm.,  thickness  11.5  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  beak  pointed  and  incurved ;  cardinal  area  concave,  he- 
coming  more  curved  towards  the  beak,  its  height  usually  between  2 
and  3  mm.,  the  inferior  portion  sloping  posteriorly  at  an  angle  of 
about  135  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply 
defined  and  curving  gently  downward  towards  the  cardinal  extremities ; 
lateral  slopes  of  the  valve  convex,  except  towards  the  cardinal  extremi- 


SPIKIPEB  :541 

ties  where  the  surface  is  usually  somewhat  compressed,  especially  in  those 
forms  with  an  extended  hinge-line,  curving  more  abruptly  to  the  cardinal 
margins  than  to  the  antero-lateral  margins,  surface  of  each  lateral  slope 
nlarked  by  from  9  to  13  simple,  rounded  plications  which  grow  fainter 
towards  the  cardinal  extremities,  the  most  usual  number  being  10  or  11 : 
mesial  sinus  originating  at  or  near  the  beak,  angular  and  sharply  defined 
at  first,  becoming  rounder  and  less  sharply  defined  anteriorly  where  it  is 
rather  shallow  or  of  moderate  depth;  near  the  beak  a  median  plication 
originates  in  the  sinus  and  continues  without  division,  becoming  gradu- 
ally stronger  to  the  anterior  margin ;  on  each  side  of  the  median  plication 
there  may  be  a  single  plication  which  is  usually,  but  not  always,  weaker 
than  the  median  one,  which  originates  in  the  bifurcation  of  the  lateral 
bounding  plication  of  the  sinuiS,;  occasionally  a  second  plication  is  present 
on  one  or  both  sides  which  originates  through  a  second  bifurcation  of  the 
bounding  plication  nearer  to  thfi  anterior  margin. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  convex- 
ity near  the  middle,  the  surface  sloping  more  abruptly  to  the  cardinal 
margin  and  becoming  somewhat  compressed  towards  the  cardinal  extrem- 
ities; mesial  fold  sharply  defined  to  the  beak,  at  first  scarcely,  or  not 
at  all,  elevated  above  the  general  surface,  becoming  gradually  elevated  an- 
teriorly where  it  is  rounded  and  of  moderate  height,  it  is  marked  by  a 
median  furrow  to  correspond  with  the  median  plication  of  the  sinus,  and 
usually  with  two  plications  on  each  side;  lateral  slopes  marked  by  plica- 
tions similar  to  those  of  the  opposite  valve  in  form  and  number. 

The  entire  surface  of  both  valves  is  marked  by  fine,  cencentric  sublam- 
ellose  markings  which  are  more  conspicuous  anteriorly,  and  sometimes  by 
occasional  stronger  lines  of  growth ;  also  by  exceedingly  minute  longitud- 
inal striae. 

Bemarks. — This  species  was  originally  described  by  Hall  as  a  variety  of 
S.  keokuk,  the  specimens  illustrated  by  him  being  from  "the  mouth  of 
Lizard  Creek,  Webster  County,  Iowa."  This  locality  is  the  site  of  the 
city  of  Fort  Dodge  at  the  present  time,  and  has  afforded  the  type 
specimens  upon  which  the  species  has  been  established  at  this  time.  The 
species  differs  from  S.  keokuk  in  its  smaller  size,  its  more  sharply  defined 
and  more  angular  mesial  sinus  towards  the  beak,  and  especially  in  the 
narrower  and  less  gibbous  umbonal  region  of  the  pedicle  valve.  The 
species  is  perhaps  most  closely  allied  to  the  more  transverse  variety  of 
S.  increbesccns,  from  the  Chester  formations,  but  among  these  Chester 
specimens  there  is  never  so  great  variation  exhibited  in  the  length  of  the 
hinge-line,  all  of  them  being  similar  to  the  more  transversely  extended 
examples  of  S.  pellaensis. 

Horizon. — Pella  beds  of  the  Ste.  Genevieve  limestone. 


342 


,\1  ISSISSIt'l'IAN     BKACIIIUl'ODA 


Spirifeb  BRECKENRIDGENSIS  n.  sp. 
Plate  XLIV,  Pigs.  20-24 

Description. — Shell  below  medium  size,  Length  and  width  sub-equal,  or 
the  length  greater  than  the  width,  the  hinge-line  shorter  than  the  greatest 
width,  the  cardinal  extremities  obtusely  angular,  the  greatest  width  near 
the  mid-length  of  the  shell.  The  dimensions  of  two  nearly  complete  in- 
dividuals are:  length  of  pedicle  valve  20  mm.  and  18  mm.,  length  of 
brachial  valve  15.5  mm.  and  1-4.4  mm.,  greatest  width  17.8  mm.  and  18 
mm.,  thickness  14  mm.  and  13  mm.,  length  of  hinge-line  14.2  mm.  and 
13.4  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  curving  abruptly  from  the  unibonal  region  to 
the  cardinal  margin  with  little  or  no  compression  towards  the  cardinal 
extremities,  and  more  gently  to  the  lateral  margins,  from  the  beak  to  the 
front  margin  the  surface  curves  with  regularly  decreasing  convexity; 
mesial  sinus  originating  at  the  beak  where  it  is  very  small  but  sharply 
denned,  becoming  rounder  and  somewhat  less  sharply  defined  anteriorly 
where  it  is  of  moderate  depth,  produced  anteriorly  in  a  rather  short, 
rounded,  lingual  extension;  the  beak  pointed  and  strongly  incurved;  the 
cardinal  area  of  moderate  height,  concave,  with  the  curvature  increasing 
towards  the  beak,  the  flatter  inferior  portion  sloping  posteriorly  at  an 
angle  of  about  135  degrees  to  the  plane  of  the  valve,  the  lateral  margins 
sharply  defined,  sloping  from  the  beak  to  the  cardinal  extremities  with  a 
slightly  sigmoidal  curvature;  the  delthyrium  rather  large,  its  base  occu- 
pying about  one-fourth  the  length  of  the  hinge-line.  Surface  of  the 
valve  marked  by  rounded  plications,  the  largest  of  which  are  usually 
those  bounding  the  mesial  sinus ;  in  the  unibonal  region  of  the  mesial 
sinus  a  median  plication  originates  as  a  faint  rib  which  grows  regularly 
larger  anteriorly  until  it  sometimes  attains  nearly  the  size  of  those 
bounding  the  sinus,  upon  each  lateral  surface  of  the  sinus  is  a  single 
somewhat  smaller  plication  which  originates  in  the  umbonal  region  from 
the  inner  margin  of  the  bounding  plication;  each  lateral  slope  of  the 
valve  is  marked  by  nine  or  ten  simple  plications  which  originate  at  or 
near  the  beak,  these  plications  grow  regularly  smaller  towards  the  cardinal 
extremities,  the  last  one  or  two  being  very  faint ;  the  surface  also  marked 
by  sublamellose,  concentric  lines  of  growth  which  become  stronger  and 
more  crowded  towards  the  front  margin. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  its  greatest  con- 
vexity near  or  a  little  posterior  to  the  middle,  the  umbo  a  little  prominent 
and  produced  slightly  posteriorly  beyond  the  hinge-line,  the  surface  a 
little  compressed  towards  the  cardinal  extremities,  aside  from  which  it 
is  rather  regularly  convex;  mesial  fold  originating  at  the  beak  as  a 
median  plication  scarcely  elevated  above  those  on  either  side,  becoming 


SPIRIFER  3-43 

moderately  elevated  in  front  and  rather  sharply  differentiated  from  t he 
lateral  slopes  of  the  valve ;  the  beak  short  and  a  little  incurved,  the  cardinal 
area  distinctly  developed  but  much  narrower  than  that  of  the  opposite 
valve,  winch  it  meets  at  an  angle  of  about  90  degrees  or  a  little  less. 
Surface  marked  by  plications  entirely  similar  in  form  and  number  to 
those  of  the  opposite  valve,  and  by  similar  concentric  markings. 

Remarks. — This  species  has  its  nearest  ally  in  S.  pellaensis,  from  which 
it  differs  in  its  proportionately  narrower  and  more  elongate  outline,  and 
in  always  having  the  hinge-line  shorter  than  the  greatest  width.  An 
occasional  specimen  of  S.  pellaensis  may  approach  very  closely  to  this 
species  in  outline,  and  so  seem  to  unite  the  two  forms  by  intermediate 
variations,  but  the  average  form  of  S.  pellcu  nsis  is  much  wider  along  the 
hinge-line  than  the  average  form  of  this  species,  a  fact  which  is  believed 
to  be  sufficient  value  to  be  considered  as  a  specific  difference.  In  the  form 
of  the  plications  and  other  characters  of  surface  ornamentation  the  two 
species  are  essentially  alike. 

Horizon. — (  nester  group. 

Spiriper  increbescens  Hall 
Plate  XL VI,  Figs.  1-12 

1858.     Spirifer  increbescens  Hall.  Geol.  Iowa.  vol.  1,  pt.  2.  p.  706.  pi.  27, 

figs.    6a-i. 
1858.     Spirifer  increbescens  var.  transn  rsalis  Hall,  Geol.  Iowa.  vol.  1,  pt.  2, 

p.   708. 
1883.     Spirif era  incn  beseem  Hall.  Rep.  N.  Y.  State  Geol.  for  1882,  pi  (30) 

55,  figs.  27-30.  pi.  (31)  56,  figs.  1-3. 
3894.     Spirifer  increbescens   Hall   and    Clarke,    Int.   to   Studv   of   Brach., 

pt.  2,  pi.  27,  figs,  8-11. 

1894.  Spirifera  increbescens  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  82. 

1895.  Spirifer  increbesct  ns  Gall  and  Clarke.  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  30, 

figs.  27-30,  pi.  31,  figs.  1-3. 
1909.     Spirifer  increbescens  Bassler,  Va.  Geol.  Surv..  Bull.  No.  II  A,  pi.  29, 

figs.  1-3. 
1911.     Spirifer  increbescens  Girty,  Bull.  U.  S.  Geol.  Survey  No.  439,  p.  68. 

Description.- — Shell  of  medium  size,  wider  than  long,  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  angular,  the  valves  sub- 
equally  convex.  The  dimensions  of  two  individuals  are :  length  31  mm. 
and  28  mm.,  greatest  width  along  the  hinge-line  40  mm.  and  44  mm., 
thickness  23  mm.  and  19  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  sloping  abruptly  from  the  more  or  less  gibbous  umbonal  region 
to  the  cardinal  margin  and  more  gently  to  the  antero-lateral  margins, 
usually  somewhat  compressed  towards  the  cardinal  extremities  but 
sometimes  with  the  fullness  extending  throughout ;  beak  pointed  and  in- 
curved ;  cardinal  area  concave,  becoming  more  curved  towards  the  beak, 


:m 


MISSISSIPPIAN     HKAClllDl'ilDA 


its  height  3  to  4  nun.,  the  inferior  portion  sloping  posteriorly  a1  an  angle 
of  aboul  135  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply 
denned  and  curving  gently  from  the  beak,  the  curvature  becoming  more 
abrupt  as  it  approaches  the  cardinal  extremities,  the  area  marked  by 
vertical  stria'  and  when  perfectly  preserved  by  fine  crenulations  along  the 
cardinal  margin;  lateral  slopes  of  the  valve  each  bearing  from  14  to  18 
rounded  plications  which  arc  usually  simple  except  that  the  second  one 
on  each  side  originates  from  the  outer  side  of  the  first  one  close  up  to  the 
beak,  and  occasionally  the  third  one  is  given  off  from  the  inner  side  of 
the  fourth;  the  mesial  sinus  originates  at  the  beak  where  it  is  sharply 
defined  and  angular,  becoming  rounder  in  the  bottom  anteriorly  and  less 
strongly  defined,  marked  by  a  median  plication  which  originates  near 
the  beak  and  continues  to  the  anterior  margin  gradually  increasing  in  size, 
each  lateral  slope  of  the  sinus  marked  by  one  plication,  or  occasionally 
two,  which  originate  from  the  inner  margins  of  the  lateral  bounding 
plications,  the  lateral  plications  are  usually  weaker  than  the  median  one 
and  when  two  are  present  the  one  which  originates  most  anteriorly  is 
much  fainter  than  the  other. 

Brachial  valve  with  its  greatest  convexity  near  the  middle,  the  surface 
sloping  more  abruptly  towards  the  cardinal  margin,  usually  somewhat, 
compressed  towards  the  cardinal  extremities;  mesial  fold  sharply  defined 
at  the  beak  but  scarcely  elevated  above  the  general  surface  of  the  valve, 
becoming  gradually  elevated  to  the  front  where  it  is  rounded  and  of 
moderate  height ;  it  is  marked  by  a  median  furrow  corresponding  with  the 
median  plication  of  the  sinus,  and  usually  with  two  plications  on  each 
side ;  the  lateral  slopes  are  marked  by  plications  similar  in  form  and 
number  to  those  of  the  opposite  valve. 

The  surface  of  both  valves  marked  by  exceedingly  fine  concentric  and 
longitudinal  lines  which  give  it  a  finely  reticulate  appearance  under  a 
lens,  and  by  coarser  lines  of  growth  which  are  sometimes  crowded 
towards  the  anterior  margin. 

Remarks. — This  species  is  most  like  S.  pellaensis,  but  is  always  larger  in 
its  adult  condition,  with  a  greater  number  of  plications,  and  does  not 
exhibit  so  great  variation  in  its  general  outline,  being  more  uniformly 
extended  along  the  hinge-line.  The  occasional  division  of  one  of  the 
larger  plications  upon  the  lateral  slopes  of  the  shell  is  also  a  feature 
which  has  not  been  observed  in  S.  pellaensis.  Immature  examples  of  8. 
increbescens,  however,  are  almost  identical  in  general  form  with  the 
smaller  species  and  may  not  possess  a  larger  number  of  plications,  but 
they  may  usually  be  recognized  as  immature  by  the  lack  of  crowding  of 
the  lines  of  growth  towards  the  anterior  margin. 

Horizon.  —  Chester  group. 


SPIRIPER  345 

Spirifer  leidvi  Norwood  and  Pratten 
Plate  XLV1I.  Pigs.  17-31 

1855.     Spirifer  Leidyi  Norwood  and  Pratten.  Jour.  Acad.  Nat.  Sci.  Phil., 

(2),  vol.  3,  p.  72,  ])1.  9,  figs.  2a-c. 
1883.     Spirifera  Leidyi  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.  (30)  55, 

figs.  25-26. 
1894.     Spirifer  Leidyi  Hall  and  Clarke,  Int.  Study  of  Brach.,  pt.  2,  pi.  27, 

figs.  16-17. 

1894.  Spirifera  leidyi  Keyes,  Mo.  Geol.  Snrv..  vol.  5,  p.  82. 

1895.  Spirifer  Leidyi  Hall  and  Clarke,  Pal.  N.  Y..  vol.  8,  pt.  2,  pi.  30. 

figs.  25-26. 

Description. — Shell  below  medium  size,  wider  than  long,  the  greatest 
width  usually  along  the  hinge-line,  the  cardinal  extremities  angnlar  o'- 
rarely  a  little  rounded,  the  valves  subequally  convex.  The  dimensions  of 
two  individuals  are:  length  21  mm.  and  17.8  mm.,  width  27.5  mm.  and  23 
mm.,  thickness  15  mm.  and  14.5  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
beak  pointed  and  incurved ;  cardinal  area  concave,  becoming  more  curved 
towards  the  beak,  its  height  2  to  3  mm.,  its  inferior  portion  sloping  pos- 
teriorly at  an  angle  of  about  115  degrees  to  the  plane  of  the  valve,  the 
lateral  margins  sharply  defined,  sloping  from  the  beak  to  the  cardinal 
extremities  in  either  a  straight  or  gently  curved  line;  lateral  slopes  of  the 
valve  convex,  becoming  a  little  compressed  towards  the  cardinal  extremi- 
ties in  the  broader  individuals,  the  surface  curving  more  abruptly  to  the 
cardinal  than  to  the  antero-lateral  margins,  each  lateral  slope  bearing 
from  7  to  10  angular  plications,  8  being  the  more  usual  number,  which 
grow  gradually  smaller  towards  the  cardinal  extremities,  the  second  pli- 
cations on  each  side,  those  next  to  the  bounding  plications  of  the  sinus, 
originate  near  the  beak  from  the  outer  side  of  the  first  plications,  the 
remaining  ones  extend  to  the  cardinal  margin  and  are  usually  simple, 
although  occasionally  one  of  the  larger  ones,  more  often  the  fourth,  bifur- 
cates near  the  beak  and  gives  origin  to  the  third  plication  from  its  inner 
sjde ;  the  mesial  sinus  originates  at  the  beak  where  it  is  angular  and 
sharply  defined,  becoming  rather  profound  anteriorly,  an  angular  median 
plication  originates  close  to  the  beak  and  continues  to  the  anterior 
margin  with  gradually  increasing  size,  each  of  the  lateral  bounding  pli- 
cations gives  rise,  from  its  inner  side  near  the  beak,  to  a  single  plication 
which  continues  without  division  to  the  anterior  margin ;  these  lateral  pli- 
cations never  attain  the  strength  of  the  median  one,  they  are  much  smaller 
and  occasionally  are  nearly  or  quite  obsolete. 

Brachial  valve  equally  or  a  little  less  convex  than  the  pedicle,  its  great- 
est convexity  near  the  middle,  the  surface  curving  more  abruptly  to  the 
cardinal  margin,  usually  becoming    somewhat    compressed    towards  the 


346 


MISSISSM'I'IAX    BRACIIHU'ODA 


cardinal  extremities;  mesial  fold  sharply  denned  at  the  beak,  becoming 
strongly  elevated  in  front,  marked  by  a  deep,  angular,  median  groove, 
which  gives  i1  a  distinctly  bifurcate  appearatlce,  on  each  lateral  slope  of 
the  fold  is  a  single,  much  weaker  plication;  lateral  slopes  of  the  valve 
marked  by  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve. 

When  perfectly  preserved  the  surface  of  the  entire  shell  is  marked  by 
minute  raised  concentric  and  longitudinal  lines  winch  gave  it  a  finely  re- 
ticulate appearance  when  examined  with  a  magnifying  glass,  the  surface 
is  also  marked  by  stronger  concentric  lines  of  growth  winch  are  some- 
times crowded  anteriorly. 

Remarks.—  In  general  form  and  size  this  species  resembles  S.  pellaensis, 
hut  it  does  not  exhibit  so  great  variation  in  outline  as  that  species.  It 
can  be  easily  distinguished  by  its  smaller  number  and  much  more  angular 
plications,  as  well  as  by  the  conspicuously  bifurcate  median  fold  of  the 
brachial  valve.  The  species  may  be  distinguished  from  immature  exam- 
ples of  8.  increbescens,  with  which  it  is  sometimes  associated,  in  much  the 
same  way  as  from  8.  pellat  nsis. 

Horizon,     ( Jhester  group. 


SniKiKKK    BIFUBCATUS    Hall 

Plate  XLVII,  Figs.  6-16 

1856.     Spirifer  bifurcata  Hall.  Trans.  Albany  Inst.,  vol.  4.  p.  8. 
1866.     Spirifer  Leidyi  var.  Merimacensis  Swallow.  Trans.  St,  Louis  Acad. 
Sei.,  vol.  2,  p.  410. 

1882.  Spirifera  bifurcata  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1, 

p.  47,  pi.  6,  figs.  13-15. 

1883.  Spirifera  bifurcata  Hall,  12th  Rep.  Geol.  Surv.  Ind.,  p.  326,  pi.  29, 

figs.  13-15. 
1895.     Spirifer  keokuk  var.  ?  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi. 

37,  figs.  13-15. 
1906.     Spirifer  bifurcatus  Beede,  30th  Rep.  Geol.  Surv.  Ind.,  p.  1314,  pi 

22,  figs   13-15 

Description. — Shell  usually  below  medium  size,  wider  than  long  or  occa- 
sionally with  the  length  and  width  subequal,  greatest  width  usually  along 
the  hinge-line,  cardinal  extremities  usually  nearly  rectangular,  sometimes 
a  little  rounded.  The  dimensions  of  two  individuals  are:  length  23  mm., 
and  12.8  mm.,  width  29  mm.  and  17  mm.,  thickness  17.5  mm.  and  9.5  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  sloping  abruptly  from  the  umbonal  region  to  the  cardinal  margin, 
more  gently  to  the  antero-lateral  margins,  not  at  all  or  hut  slightly  com- 
pressed towards  the  cardinal  extremities;  beak  pointed  and  incurved; 
cardinal  area  concave,  becoming  more  curved  towards  the  beak.  2  to  4 
mm.  high,  the  inferior  portion  sloping  posteriorly  at  an  angle  of  about 


SPIRIFEB  347 

115  degrees  to  the  plane  of  the  valve,  the  lateral  margins  sharply  defined, 
sloping  from  the  beak  to  the  cardinal  extremities,  the  surface  vertically 
striated  ;  lateral  slopes  of  the  valve  each  bearing  from  5  to  8  simple  angular 
plications,  6  or  7  being  the  most  usual  number,  which  become  progressive- 
ly weaker  towards  the  cardinal  extremities;  mesial  sinus  well  defined  to 
the  beak,  becoming  more  or  less  profound  anteriorly,  marked  by  an  angu- 
lar median  plication  which  originates  near  the  beak  and  continues  to  the 
anterior  margin  with  gradually  increasing  size,  becoming  nearly  as  strong 
as  the  larger  plications  upon  the  lateral  slopes;  in  the  larger  individuals 
a  single  faint  plication  is  sometimes  present  upon  each  of  the  lateral 
slopes  of  the  sinus,  originating  from  the  lateral  bounding  plications. 

Brachial  valve  with  its  greatest  convexity  near  the  middle,  the  surface 
sloping  more  abruptly  to  the  cardinal  margin,  sometimes  becoming  a  little 
compressed  towards  the  cardinal  extremities ;  mesial  fold  well  defined  to 
the  beak,  moderately  or  rather  highly  elevated  anteriorly,  marked  by  a 
profound  median  furrow  which  divides  it  into  two  sharply  angular  pli- 
cations, occasionally  a  single  much  fainter  plication  is  present  upon  each 
lateral  slope  of  the  fold  in  the  larger  individuals;  the  lateral  slopes  are 
marked  by  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve. 

Remarks. — This  species  was  originally  described  from  dwarfed  individ- 
uals from  the  Spergen  Hill  fauna,  the  type  specimen  not  exceeding  2.5  mm. 
in  width.  It  occurs  very  generally  in  the  Salem  limestone,  however,  and 
is  usually  of  much  larger  size  than  the  type.  The  species  is  most  closely 
allied  to  S.  leidyi,  in  fact  it  was  described  by  Swallow  at  one  time  as  a 
variety  of  that  species,  S.  leidyi  var  merimacensis,  and  "Whitfield  has  ex- 
pressed the  opinion  that  the  two  species  are  not  distinct.  A  careful  study 
by  the  writer  of  many  specimens  of  both  species  has  forced  the  conclusion 
that  the  two  forms  are  well  worthy  of  recognition  as  distinct  species,  al- 
though they  are  doiibtless  genetically  related,  8.  bifurcatus  being  the  earlier 
and  8.  leidyi  the  later  form.  In  8.  Mfurcatus  the  plications  are  usually 
less  in  number  and  somewhat  coarser,  and  the  lateral  plications  of  the 
fold  and  sinus  are  usually  obsolete  except  in  the  larger  individuals.  In 
8.  leidyi  the  lateral  plications  of  the  fold  and  sinus  are  always  present  ex- 
cept in  very  rare  instances.  An  occasional  example  of  S.  bifurcatus  may 
be  almost  identical  in  its  characters  with  some  examples  of  S.  leidyi,  but 
when  one  compares  the  normal  or  average  condition  of  a  large  number 
of  individuals  of  both  species,  there  is  a  distinct  difference  between  the 
two,  a  difference  which  is  sufficiently  marked  to  be  of  specific  rank, 
especially  when  the  time  relations  of  the  two  are  taken  into  consideration. 

Horizon. — Salem  limestone. 


■    18  Mississippi. \\    BBACHIOPODA 

Si'ikii'kk  litton]  Swallow 

Plate  L,  Pigs.  1-5 

1860.     Spirifer  Littowi  Swallow.  Trans.  St.  Louis  Acad.  Sci.,  vol.  1,  p.  (i4G. 

Description. — Shell  below  medium  size,  longer  than  wide,  the  hinge-line 
shorter  than  the  greatest  width,  the  cardinal  extremities  rounded.  The 
dimensions  of  a  nearly  perfect  specimen  are:  length  of  pedicle  valve  20.4 
mm.,  length  of  brachial  valve  17  nun.,  greatesl  width  2'A  nun.,  length  of 
hinge-line   16  nun.,  thickness  lf).:{  nun.,  heighl   of  cardinal  area  3.5  nun. 

Pedicle  valve  rather  strongly  convex,  the  greatesl  depth  towards  the 
umbo,  the  surface  curving  abruptly  to  the  cardinal  margin,  more  gently 
to  the  lateral  and  anterior  margins,  not  compressed  towards  the  cardinal 
extremities:  beak  small,  pointed  and  lather  strongly  incurved;  the  car- 
dinal area  of  moderate  height,  rather  strongly  arched,  the  curvature  be- 
coming greater  towards  the  beak,  the  Lateral  margins  not  very  sharply 
defined,  the  delthyrium  large,  about  as  wide  as  high;  mesial  sinus  origin- 
ating at  the  beak  as  a  narrow,  hut  well-defined  depression,  becoming 
rather  broad  and  moderately  deep  to  the  front  where  it  is  somewhat  pro- 
duced in  an  anterior  extension  of  the  valve,  it  is  marked  by  a  mesial  pli- 
cation which  originates  near  the  beak  as  a  very  fine,  elevated  line,  becom- 
ing rather  broadly  rounded,  but  not  very  high  towards  the  front,  and  by  a 
single,  fainter,  sometimes  nearly  obsolete  plication,  upon  each  side,  which 
originates  from  the  inner  margin  of  the  lateral  bounding  plications;  the 
lateral  slopes  regularly  convex,  each  marked  by  from  eight  to  ten  simple, 
rounded  plications  which  grow  successively  smaller  towards  the  cardinal 
extremities. 

Brachial  valve  subelliptical  in  outline,  its  convexity  about  equal  to  or 
a  little  less  than  that  of  the  pedicle  valve,  its  greatest  depth  near  or  pos- 
terior to  the  middle,  the  umbonal  region  rather  prominent  and  projecting 
beyond  the  cardinal  margin,  the  surface  curving  abruptly  to  the  cardinal 
margin  and  more  gently  to  the  lateral  and  anterior  margins,  slightly  com- 
pressed towards  the  cardinal  extremities ;  cardinal  area  narrow ;  the  beak 
rather  strongly  incurved ;  mesial  fold  originating  at  the  beak  as  a  flat- 
tened, scarcely  elevated  plication,  it  is  well  defined  and  becomes  mod- 
erately elevated  in  front,  with  a  rather  broadly  rounded  mesial  depres- 
sion and  usually  a  single  fainter  depression  upon  each  side;  the  lateral 
slopes  marked  by  simple,  rounded  plications  entirely  similar  to  those  of 
the  opposite  valve. 

The  finer  surface  markings  consist  of  rather  inconspicuous  concentric 
lines  of  growth,  an  occasional  one  of  which  is  somewhat  stronger  than  the 
others,  and  by  an  exceedingly  fine  reticulate  marking  which  is  only  vis- 
ible upon  perfectly  preserved  surfaces. 


SPIRIPER  349 

IU  marks. — This  is  one  of  the  species  which  lias  never  previously  been 
illustrated,  and  which  has  not  commonly  been  recognized.  The  type  spec- 
imens have  been  lost,  but  the  shells  here  referred  to  the  species  agree 
well  with  the  original  definition  and  occur  in  the  St.  Louis  limestone, 
from  which  formation  the  types  of  the  species  were  reported.  The  species 
resembles  S.  bifurcatus  as  closely  as  any  other,  but  may  be  distinguished 
by  its  much  less  angular  plications.  It  differs  from  8.  pellaensis  in  its 
shorter  hinge-line,  rounded  cardinal  extremities,  and  in  its  stronger  pli- 
cations, especially  the  stronger  median  plication  of  the  mesial  sinus. 

Horizon.- — St.  Louis  limestone. 

Spiripkr  marsh allensis  n.  sp. 
Plate  L,  Figs.  13-14 

Description. — Shell  small,  wider  than  long,  the  hinge-line  shorter  than 
the  greatest  width  of  the  shell,  the  cardinal  extremities  rounded.  The 
dimensions  of  a  brachial  valve  are:  length  12  mm.,  width  18  mm.,  length 
of  hinge-line  ±14  mm.,  convexity  6  mm.     The  pedicle  valve  not  known. 

Brachial  valve  transversely  subelliptical  in  outline,  moderately  convex, 
the  greatest  convexity  near  the  middle,  subcarinate  along  the  median  line, 
the  umbonal  region  slightly  produced  beyond  the  hinge-line ;  mesial  fold 
defined  to  the  beak,  scarcely  elevated  in  the  umbonal  region,  becoming 
moderately  elevated  anteriorly  but  not  sharply  differentiated  from  the 
general  convexity  of  the  valve,  it  is  rounded  in  contour  and  is  marked 
anteriorly  by  four  obscure  plications  which  unite  into  a  single  one  in 
passing  to  the  beak;  lateral  slopes  convex  antero-posteriorly,  the  curva- 
ture a  little  more  abrupt  to  the  cardinal  margin,  the  slope  from  the  middle 
of  the  mesial  fold  to  the  lateral  margin  at  the  widest  part  of  the  shell  is 
very  slightly  convex  or  is  nearly  a  straight  line,  giving  the  valve  its  sub- 
carinate aspect,  the  surface  is  slightly  compressed  towards  the  cardinal 
extremities,  each  slope  marked  by  9  or  10  simple,  depressed,  rounded 
plications  separated  by  rounded  furrows  about  equaling  the  plications 
in  width. 

The  minute  surface  markings  of  the  specimens  examined  are  not  per- 
fectly preserved,  but  the  shell  is  apparently  granulose,  no  concentric  or 
radiating  stria-  of  any  sort  are  indicated. 

Remarks.— In  size  and  general  form  this  species  resembles  S.  orestes 
H.  and  W.,  from  the  Upper  Devonian  of  Rockford,  Iowa,  but  it  may  be 
distinguished  by  its  less  elevated  and  less  angular  median  fold  and  by 
the  more  rounded  cardinal  extremities. 

Horizon.— Kinderhook. 


350  MISSISSIPFIAN    BRACHIOPODA 

SPIBIFER   KEOKUK    Hall 

Plate  XLIX,  Pigs.  1-14 

Ls.r>L;.     Spirifer  attenuatus  Owen.  Geol.  Rep.  Wis.,  Iowa,  and  .Minn.,  tab. 

3A,  fig.  8. 
1858.     Spirifer  keokuk  Hall.  Geol.  Iowa.  vol.  1,  pt.  2,  p.  642,  pi.  20,  figs. 

3a-d,  2d. 
1883.     Spirifera  Keokuk  Hall.  Rep.  X.  V.  Slate  Geol.  for  1882,  pi   (30)  55, 

figs.   21-22    (not    figs.   23-24). 
1894.     Spirifer  Keokuk  Hall  and  Clarke,  Int.  Study  of  Brach.,  pt.  2,  pi. 

27.   Iit;s.  14-15. 

1894.  Spirifera  keokuk  Keyes,  Mfo.  Geol.  Surv.,  vol.  5,  p.  81,  pi.  40,  fig.  2. 

1895.  Spirifer  Keokuk  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  30, 

figs.  21-22  (not  figs.  23-24). 

Description.  Shell  of  medium  size,  wider  than  long,  greatest  width  at 
or  near  (he  hinge-line,  the  cardinal  extremities  more  or  less  nearly 
rectangular,  sometimes  rounded  in  the  narrower  specimens.  The  dimen- 
sions of  two  examples  are:  length  26.5  mm.  and  26.8  mm.,  width  31  mm. 
and  35  mm.,  thickness  1.9.5  mm.  and  19.5  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbonal  region  broadly  convex,  the  surface  more  or  less 
compressed  towards  the  cardinal  extremities;  beak  pointed  and  rather 
strongly  incurved ;  cardinal  area  concave,  becoming  more  strongly  curved 
as  it  approaches  the  beak,  the  inferior  portion  sloping  posteriorly  at  an 
angle  of  about  135  degrees  to  the  plane  of  the  valve,  about  4  to  5  mm. 
in  height,  the  lateral  margins  sharply  defined,  sloping  from  the  beak 
to  the  cardinal  extremities  first  with  a  convex  and  then  with  a  concave 
curvature ;  lateral  slopes  of  the  valve  convex  on  either  side  of  the  sinus, 
curving  abruptly  to  the  cardinal  margin,  the  curvature  becoming  concave 
as  it  approaches  the  cardinal  extremities,  each  marked  by  from  11  to  15 
rounded  plications  which  become  progressively  smaller  towards  the  car- 
dinal extremities,  all  of  them  are  simple  except  occasionally  those  which 
form  the  lateral  boundaries  of  the  sinus ;  mesial  sinus  shallow'  and  rounded 
in  the  bottom  near  the  beak,  becoming  deeper  and  broader  anteriorly, 
sometimes  produced  anteriorly  into  a  conspicuous  nasute  extension ;  near 
the  beak  a  single  median  plication  originates  which  usually  continues  to 
the  anterior  margin  as  a  simple  rounded  rib,  increasing  regularly  in  size, 
occasionally  this  median  rib  bifurcates  and  continues  to  the  anterior 
margin  as  two  smaller  rounded  plications ;  on  each  side  of  the  median  rib 
may  be  seen  one  or  perhaps  two,  usually  weaker,  plications  upon  the  lateral 
slopes  of  the  sinus,  which  originate  from  the  inner  lateral  margins  of  the 
plications  bounding  the  sinus. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  greatest  convexity 
near  the  middle,  the  surface  sloping  more  abruptly  from  the  umbo  to  the 
cardinal  margin,  becoming  somewhat  compressed   towards  the  cardinal 


SPIRIFEB  351 

extremities;  mesial  fold  scarcely  elevated  above  the  general  surface  near 
the  beak,  often  becoming  rather  highly  elevated  anteriorly,  always  rounded, 
marked  by  a  shallow  rounded  median  furrow  corresponding  with  the 
median  plication  of  the  sinus,  and  by  two  or  sometimes  three  plications 
on  each  side;  lateral  slopes  marked  by  rounded  plications  which  are 
similar  in  form  and  number  with  those  of  the  opposite  valve. 

Surface  of  both  valves  marked  b<3r  fine  concentric  lines  which  are  more 
crowded  and  conspicuous  towards  the  anterior  margin  and  by  occasional 
stronger  lines  of  growth,  also  by  very  minute  longitudinal  stria1  which 
give  to  the  perfectly  preserved  surface,  when  viewed  under  a  lens,  a 
finely  reticulate  appearance. 

"Remarks. — Shells  from  various  horizons  in  the  Mississippian  have  com- 
monly been  referred  to  S.  heokuk,  hut  many  of  them  have  been  incorrectly 
identified.  The  species  seems  to  be  closely  confined  to  the  Keokuk  lime- 
stone and  often  occurs  in  great  numbers  in  one  zone  near  the  summit  of 
the  limestone  beds  of  the  formation.  The  species  may  be  easily  distin- 
guished from  other  related  forms  by  reason  of  the  rotund  convexity  of 
the  umbonal  region  of  the  pedicle  valve,  and  by  the  less  angular  sinus 
of  the  same  valve  near  the  beak. 

Horizon.— Keokuk  limestone. 

Spirifer  floydensis  n.  sp. 
Plate  XLIX,  Figs.  15-19 

Description. — Shell  of  medium  size,  wider  than  long,  the  greatest  width 
at  or  near  the  hinge-line,  the  cardinal  extremities  nearly  rectangular. 
The  dimensions  of  two  individuals  are:  length  of  pedicle  valve  35.5  mm. 
and  31.5  mm.,  length  of  brachial  valve  31  mm.  and  25  mm.,  width  43  mm. 
and  35  mm.,  thickness  ±24  mm.  and  22  mm.,  height  of  cardinal  area  4  mm. 
and  3.5  mm. 

Pedicle  valve  strongly  convex  in  the  umbonal  region,  the  greatest  con- 
vexity posterior  to  the  middle,  the  surface  curving  abruptly  to  the  car- 
dinal margin,  more  gently  to  the  antero-lateral  margins,  somewhat  com- 
pressed towards  the  cardinal  extremities;  beak  small,  attenuate,  incurved; 
cardinal  area  of  moderate  height,  arched,  the  curvature  increasing  to- 
wards the  beak,  the  lateral  margins  sharply  defined,  sloping  from  the 
beak  to  the  cardinal  extremities  in  nearly  a  straight  line  or  with  a  gently 
concave  curve;  lateral  slopes  convex  towards  the  median  sinus,  becoming 
slightly  compressed  towards  the  cardinal  extremities,  each  marked  by 
from  15  to  20  depressed  rounded  plications,  one  or  more  of  which  may 
bifurcate  between  the  umbonal  region  and  the  anterior  margin,  they  grow 
successively  smaller  towards  the  cardinal  extremities,  the  last  3  or  4 
being  very  faint  or  sometimes  almost  obsolete;  mesial  sinus  originating 
at  the  beak  where  it  is  simple  and  sharply  defined,  anteriorly  it  becomes 


352  MISSISSII'IMAN    BRACHIOPODA 

ill-defined  and  plicated,  a  median  plication  originates  near  the  beak  and 
continues  withoul  division  to  the  anterior  margin,  on  each  side  there 
arc  4  or  5  plications  which  originate  From  the  inner  margins  of  the  bound- 
ing plications  or  through  the  bifurcation  of  such  plications. 

Brachial  valve  about  as  convex  as  the  pedicle,  the  greatest  convexity 
near  the  middle,  the  surface  becoming  compressed  towards  the  cardinal 
extremities;  mesial  fold  defined  to  the  beak,  slightly  elevated  above  the 
general  surface  of  the  valve  in  the  urn  bona  I  region,  becoming  rather  highly 
elevated  in  front,  rounded  or  subangular  along  the  median  line,  marked 
by  plications  similar  to  those  of  the  sinus  of  the  pedicle  valve;  lateral 
slopes  most  convex  towards  the  umbona]  region,  marked  by  plications 
entirely  similar  in  form  and  number  to  those  of  the  Opposite  valve. 

Remarks.  This  species  resembles  S.  keokuk  in  some  respects,  but  besides 
usually  growing  to  a  larger  size,  its  plications  are  more  numerous  on 
both  the  lateral  slopes  and  the  fold  and  sinus,  they  bifurcate  more  fre- 
quently and  are  not  so  strongly  elevated  as  in  that  species.  The  minute 
surface  markings  of  the  shell  are  not  sufficiently  well  preserved  on  either 
of  the  specimens  examined  to  determine  all  their  characters,  but  so  far 
as  they  are  preserved  they  are  not,  unlike  those  of  8.  keohuk. 

Horizon. — Knobstone  formation  of  Indiana. 

Spiriper  indianensis  n.  sp. 
Plate  L,  Figs.  6-12 

Description. — Shell  below  medium  size,  longer  than  wide,  the  greatest 
width  a  little  in  front  of  the  cardinal  line,  the  cardinal  extremities  ob 
tusely  angular  or  rounded.  The  dimensions  of  a  nearly  complete  example 
are:  length  28.5  mm.,  width  22.5  mm.,  thickness  19  mm.;  the  dimensions 
of  a  perfect  pedicle  valve  are:  length  28  mm.,  width  25  mm.,  length  of 
hinge-line  20  mm.,  convexity  12  mm. 

Pedicle  valve  with  its  greatest  convexity  near  or  a  little  posterior  to  the 
middle,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  margin,  more  gently  to  the  antero-lateral  margins,  the  convexity 
of  the  valve  extending  out  to  the  cardinal  extremities;  beak  pointed  and 
strongly  incurved;  cardinal  area  concave,  becoming  more  curved  towards 
the  beak,  its  height  4  to  5  mm.,  its  inferior  portion  sloping  posteriorly  at 
an  angle  of  140  degrees  or  more  to  the  plane  of  the  valve,  the  lateral  mar- 
gins defined,  sloping  from  the  beak  to  the  cardinal  extremities  with  a 
gently  convex  curve,  the  surface  marked  by  vertical  striae ;  lateral  slopes 
of  the  valve  each  bearing  9  or  10  simple,  low,  rounded  plications  which 
grow  gradually  smaller  towards  the  cardinal  extremities ;  the  mesial  sinus 
originates  at  the  beak  where  it  is  shallow  and  rounded  in  the  bottom,  it 
becomes  relatively  shallower  in  the  anterior  half  of  the  shell  where  it 
is  often  rather  ill-defined,  its  anterior  margin  is  produced  into  a  nasute 


SPIBIFER  353 

extension,  it  is  marked  by  a  median  plication  which  originates  near  the 
beak,  or  at  least  in  the  umbonal  region,  and  continues  to  the  anterior 
margin  with  gradually  increasing  strength,  sometimes  this  median  plica- 
tion is  the  only  one  present  in  the  sinus,  but  not  infrequently  there  is  a 
single  lateral  plication  on  each  side  which  originates  from  the  inner 
margins  of  the  bounding  plications,  making  three  in  all,  the  median 
plication  is  about  equal  in  strength  to  the  larger  of  the  plications  on  the 
lateral  slopes  of  the  valve,  the  other  two,  when  present,  being  somewhat 
weaker. 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity 
posterior  to  the  middle,  the  beak  sharply  pointed,  extending  a  little  beyond 
the  hinge-line  and  slightly  incurved  over  the  narrow  cardinal  area,  the 
surface  of  the  valve  sloping  more  abruptly  to  the  cardinal  margin,  slightly 
or  not  at  all  compressed  towards  the  cardinal  extremities ;  mesial  fold 
defined  to  the  beak,  but  slightly  elevated  posteriorly,  attaining  a  moderate 
height  towards  the  anterior  margin,  where  it  has  a  rounded  contour, 
marked  by  a  single,  shallow,  rounded,  median  furrow,  and  sometimes  by  a 
still  fainter  one  upon  each  lateral  slope;  the  lateral  slopes  are  marked 
by  plications  which  are  similar  in  size  and  number  to  those  of  the  opposite 
valve. 

The  more  minute  surface  markings  are  not  well  preserved  upon  the 
specimens,  but  there  are  fine  concentric  lines  of  growth  towards  the 
anterior  margin,  and  occasionally  stronger  ones. 

Hi  marks.  —  S.  indianensis  resembles  S.  keokuk  in  its  type  of  surface 
markings,  but  it  can  be  distinguished  at  once  from  that  species  by  its 
elongate  form.  This  elongation  of  the  shell  is  rather  an  unusual  form 
among  the  species  of  Spirifer  in  our  Mississippian  faunas,  and  the  species 
may  be  recognized  by  this  character  alone,  as  there  is  no  other  closely 
allied  species,  with  such  a  form. 

Horizon. — Keokuk  (Harrodsburg  limestone  of  Indiana). 

Spirifer  kostellatus  Hall 
Plate  XL VIII,  Figs.  6-16 

1858.     Spirifer  rostellatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  641,  pi.  20, 
figs.  2a-c. 

1894.  Spirifera  rostellata  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  82. 

1895.  Spirifer  rostellatus  Ha'll  and  Clarke,  Pal.  X.  Y.,  vol.  8,  pt.  2,  pi.  32, 

fig.  5. 

Description. — Shell  of  medium  size,  subovate  to  subelliptical  in  outline, 
varying  from  longer  than  wide  to  wider  than  long,  the  greatest  width 
near  the  mid-length  of  the  shell,  the  hinge-line  much  shorter  than  the 
greatest  width,  the  cardinal  extremities  rounded.  The  dimensions  of  a 
complete   individual,   the  holotype   of   the  species,   are:   length   27.5   mm., 

—12 


254 


MISSISSIPPI  AN    HKACIIIlironA 


width  2<>  mm.,  thickness  15.5  mm.,  Length  of  binge-line  13  mm.,  height  of 
cardinal  area  ■!  nun.  Other  specimens  arc  frequently  proportionally  much 
broader. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
convexity  extending  out  to  the  cardinal  extremities,  the  umbonal  region 
prominent  but  rather  narrow,  produced  posteriorly  beyond  the  binge- 
line,  the  surface  sloping  abruptly  from  the  umhonal  region  to  the  cardinal 
margin,  more  gently  to  the  lateral  and  anterior  margins;  beak  sharply 
pointed,  narrow  and  incurved,  its  tip  reaching  the  plane  of  the  valve; 
cardinal  area  small,  arched,  the  curvature  becoming  greater  towards  the 
beak,  the  lateral  margins  defined,  sloping  steeply  from  the  beak  to  the 
cardinal  extremities,  the  dclthyrium  large,  broader  than  high,  its  width 
along  the  binge-line  a  little  less  than  one-half  the  total  length  of  the 
binge-line;  lateral  slopes  each  marked  by  18  to  20  rounded  plications 
which  increase  by  bifurcation  in  the  umbonal  region  and  less  frequently 
towards  the  front,  they  grow  successively  smaller  towards  the  cardinal 
extremities  where  the  last  ones  are  nearly  obsolete;  mesial  sinus  narrow 
and  well  defined  towards  the  beak,  where  it  is  without  plications,  anter- 
iorly it  is  ill-defined,  shallow  and  rounded  in  the  bottom,  a  median 
plication  originates  in  the  umbonal  region  which  inci'eases  by  bifurcation 
to  two  or  three  at  the  anterior  margin,  each  lateral  slope  of  the  sinus 
bears  about  three  plications  similar  in  form  and  size  to  the  middle  ones, 
one  or  two  of  which  originate  from  the  lateral  margins  of  the  bounding 
plications  and  the  Others  from  the  bifurcation  of  these  original  ones. 

Brachial  valve  wider  than  long,  less  convex  than  the  pedicle,  its 
greatest  convexity  near  the  middle,  sometimes  a  little  compressed  towards 
the  cardinal  extremities;  mesial  fold  defined  to  the  beak  but  scarcely 
elevated  above  the  general  surface  back  of  the  middle  of  the  valve,  and 
only  a  little  elevated  in  front  where  it  is  rounded  in  contour,  marked  Im- 
plications similar  in  form  and  number  to  those  of  the  sinus  in  the  opposite 
valve,  all  of  which  originate  through  the  division  of  the  single  original 
plication  at  the  beak;  the  lateral  slopes  gently  convex,  marked  by  plica- 
lions  similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  well  preserved,  but 
exceedingly  fine  longitudinal  stria'  are  suggested  at  one  point  upon  the 
type  specimen,  and  perhaps  also  some  minute  concentric  lines.  A  few 
concentric  lines  of  growth  are  usually  present. 

Remarks. — This  shell  can  be  easily  recognized  by  its  ovoid  form,  its 
short  hinge-line  and  its  narrow  and  protuberant  umbonal  region.  In  its 
surface  markings  it  apparently  resembles  S.  grimesi  and  S.  logani,  and  its 
general  form  is  in  some  respects  a  miniature  of  8.  grimesi  but  with  pro- 
portionally shorter  hinge-line  and  finer  plications. 

Horizon.  —  Keokuk  limestone. 


SPIRIFER  355 

Spiriper  tentjimarginatus  Hall 

Plate  XLVIII,  Figs.  1-5 

1858.     Spirifi  r  t<  nuimarginatus  Ball,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  641,  pi.  20, 

figs.  la-c. 
1883.     Spirifera  tenuimarginata  Ball,  Rep.  N.  Y.  State  Geol.   for  1882, 

pi.  (32)  57.  figs.  4-6. 
1895.     Spirifi  /■  tenuimarginatus  Ball  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2. 
pi.  32,  figs.  4,  6. 

Description.— Shell  small,  subovate  or  subrhombie  in  outline,  wider  than 
long,  the  greatest  width  at  or  close  to  the  hinge-line,  the  hinge-line  about 
equaling  the  greatest  width  of  the  shell,  the  cardinal  extremities  sub- 
angular.  The  dimensions  of  the  holotype  are:  length  of  pedicle  valve  19.5 
mm.,  length  of  brachial  valve  16.5  mm.,  width  21.8  mm.,  thickness  11.8 
min..  height  of  cardinal  area  2.5  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  a  little  compressed  towards  the  cardinal  extremities,  the  umbonal 
region  prominent,  produced  posteriorly  somewhat  beyond  the  hinge-line, 
(he  surface  sloping  abruptly  to  the  cardinal  margin  from  the  umbonal 
region,  more  gently  to  the  antero-lateral  margins;  beak  sharply  pointed, 
narrow  and  incurved;  cardinal  area  small,  arched,  the  curvature  be- 
coming greater  towards  the  beak,  the  lateral  margins  sharply  defined, 
sloping  steeply  from  the  beak  to  the  cardinal  extremities,  the  delthyriuni 
large,  broader  than  high;  lateral  slopes  each  marked  by  about  20  angular 
plications  with  frequent  bifurcations ;  mesial  sinus  ill-defined  anteriorly, 
more  sharply  defined  towards  the  beak,  rounded  in  the  bottom,  shallow 
or  of  moderate  depth,  marked  by  about  12  plications  similar  to  those 
on  the  lateral  slopes,  one  plication  originates  at  the  median  line  near  the 
beak  and  divides  into  two  or  three  before  reaching  the  anterior  margin. 
the  lateral  plications  originate  from  the  inner  margins  of  the  bounding 
plications  or  through  the  bifurcation  of  plications  so  originating. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  the  surface  compressed  towards  the  cardinal 
extremities;  mesial  fold  defined  to  the  beak  but  scarcely  elevated  above 
the  general  surface  in  the  posterior  third  of  the  valve,  bcoming  strongly 
elevated  in  front,  rounded  in  contour  in  the  middle  of  the  shell,  becoming 
subangular  towards  the  front,  marked  by  plications  similar  in  form  and 
Dumber  to  those  of  the  sinus  of  the  opposite  valve,  all  of  which  originate 
through  the  division  of  the  single  original  plication  at  the  beak;  lateral 
slopes  gently  convex,  more  or  less  flattened  towards  the  cardinal  ex- 
tremities, marked  by  angular,  bifurcating  plications  similar  to  those  of 
the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  well  preserved,  but 
rather  tine,  concentric,  perhaps  sublamellose  lines  of  growth  are  suggested, 
with  a  few  stronger,  concentric  lines  of  growth. 


35G  .Mlssissii'i'l.W   BRACHIOPODA 

Remarks,  This  species  is  known  to  the  writer  only  through  a  sulphur 
(■;ist  of  the  holotype.  The  entire  asped  of  this  specimen  strongly  suggests 
a  small  and  exceptionally  narrow  example  df  S.  tenuicostatus,  and  it  is 
not  unlikely  thai  such  an  interpretation  of  the  specimen  may  be  correct. 
Examples  of  8.  rostellatus  have  sometimes  been  identified  as  S.  tenu/imar- 
ginatus,  due  to  the  fact  thai  the  figured  type  of  S.  rostellatus  is  an  un- 
usually narrow  specimen  of  the  species.  The  type  of  S.  tenuimarginatus 
differs  notably  from  8.  rostellatus  in  its  much  finer  and  more  angular  plica- 
tions and  its  proportionally  much  more  elongate  hinge-line. 

Horizon.      Keokuk  limestone. 

SPIEIFEB   SUBROTUNDUS   n.    noni. 

Plate  I,.  Pigs.  15-22 

1858.  Spirifer  subrotundatus  Hall,  Geol.  Surv.  Iowa,  vol.  1,  pt.  2,  p.  521, 
pi.  7,  tig.  8.    (Not  8.  subrotundatus  McCoy,  1855.) 

1900.  Spirifer  subrotundatus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 
p.  7G,  pi.  2,  figs.  8-10. 

Description. — Shell  of  medium  size,  subcircular,  subovate  or  subellipti- 
cal  in  outline,  the  width  equal  to,  greater  than,  or  less  than  the  length, 
the  hinge-line  much  shorter  than  the  greatest  width  of  the  shell,  the  car- 
dinal extremities  rounded,  the  greatest  width  of  the  shell  near  its  mid- 
length.  The  dimensions  of  two  individuals  are:  length  of  pedicle  valve 
32  mm.  and  35  mm.,  length  of  brachial  valve  26  mm.  and  28  mm.,  greatest 
width  37  mm.  and  33  mm.,  thickness  18  mm.  and  24  mm.,  height  of  car- 
dinal area  ±4.5  mm.  and  ±4  mm. 

Pedicle  valve  more  or  less  strongly  convex,  the  convexity  extending 
out  to  the  cardinal  extremities,  the  surface  curving  abruptly  from  the 
umbonal  region  to  the  cardinal  margin  and  more  gently  to  the  antero- 
lateral margins ;  beak  rather  obtuse  in  the  casts  and  more  or  less  incurved  ; 
cardinal  area  of  medium  height,  more  or  less  arched,  the  lateral  margins 
defined  but  doubtless  less  defined  in  the  casts  than  in  the  shell  itself, 
sloping  from  the  beak  to  the  cardinal  extremities ;  lateral  slopes  each 
marked  by  25  or  more  depressed,  bifurcating  plications  which  become 
faint  or  almost  obsolete  towards  the  cardinal  extremities ;  mesial  sinus  ill- 
defined,  shallow,  rounded,  sometimes  scarcely  more  than  a  flattening  of 
the  median  portion  of  the  valve,  marked  by  10  or  12  plications  similar  in 
every  respect  to  those  of  the  lateral  slopes. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity near  or  posterior  to  the  middle,  the  surface  curving  rather  ab- 
ruptly from  the  umbonal  region  to  the  cardinal  margin,  and  more  gently 
to  the  antero-lateral  margins,  sometimes  a  little  compressed  towards  the 
cardinal  extremities ;  mesial  fold  low,  ill-defined,  scarcely  raised  above 
the  general  surface  of  the    valve    except    sometimes    towards    the  front, 


SPIRIFER  357 

marked  by  plications  similar  in  form  and  number  to  those  of  the  opposite 
^alve;  the  lateral  slopes  marked  by  plications  similar  in  all  ways  to  those 
of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  preserved  in  the  con- 
dition of  preservation  in  which  all  the  examples  have  been  found.  Some 
concentric  lines  of  growth  of  greater  or  less  strength  occur  at  irregular 
intervals. 

Remarks. — This  species  has  been  observed  only  in  the  condition  of  in- 
ternal easts  in  a  fine-grained  sandstone,  a  condition  in  which  the  more 
minute  markings  of  the  shell  cannot  be  recognized.  It  is  therefore  im- 
possible to  determine  whether  or  not  the  shell  was  marked  by  minute 
longitudinal  stria3  or  corrugations  such  as  are  present  in  S.  grimesi,  S. 
iogani,  and  S.  striatiformis.  In  its  completely  plicated  shell  with  similar, 
bifurcating  plications  on  both  fold  and  sinus  and  on  the  lateral  slopes  of 
the  valves,  the  species  resembles  the  above  named  forms,  but  it  differs 
essentially  from  all  of  these  in  its  size  and  proportions. 

Hall's  original  designation  of  the  species,  S.  subrotundaius,  proves  to 
have  been  preoccupied  by  McCoy,  in  consequence  of  which  it  is  here 
called  8.  sitbrotitndus. 

Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 

Spirifer  maplensis  n.  sp. 
Plate  LI,  Figs.  3-8 

Description. — Shell  of  medium  size,  usually  longer  than  wide,  and  longi- 
tudinally subelliptical  in  outline,  but  occasionally  individuals  occur  in 
which  the  length  and  breadth  are  nearly  equal ;  the  hinge-line  shorter 
than  the  greatest  width  of  the  shell,  the  cardinal  extremities  rounded. 
The  dimensions  of  a  medium  sized  pedicle  valve  are:  length  29  mm., 
width  22  mm.,  convexity  10  mm.,  length  of  hinge-line  14  mm.  The  dimen- 
sions of  a  brachial  valve  are:  length  25  mm.,  width  21  mm.,  convexity  6 
mm.  The  dimensions  of  the  largest  example  observed,  a  pedicle  valve, 
are :  length  37  mm.,  width  37  mm.,  convexity  16  mm. 

Pedicle  valve  strongly  and  regularly  convex,  the  convexity  extending 
out  to  the  cardinal  extremities,  the  greatest  convexity  near  or  posterior 
to  the  middle;  beak  obtuse  in  the  internal  casts,  reaching  but  a  short  dis- 
tance  back  of  the  hinge-line;  character  of  the  cardinal  area  not  well 
shown  in  the  specimens,  but  it  is  evidently  low  and  small ;  lateral  slopes 
of  the  valve  sloping  abruptly  with  a  convex  curvature  from  near  the 
mesial  sinus  to  the  lateral  margins,  the  surface  becoming  nearly  vertical 
to  the  plane  of  the  valve  near  the  margin,  the  curvature  to  the  cardinal 
margin  more  abrupt  than  to  the  lateral  margin,  each  lateral  slope  marked 
by  from  20  to  25  flattened,  radiating  plications  which  increase  by  bifur- 
cation in  passing  towards  the  anterior  margin,  and  decrease  in  size  to- 


358  .MISSISSll'I'l AN    BBACHIOPODA 

wards  1 1 1  < »  cardinal  extremities;  mesial  sinus  shallow,  narrow,  rounded  in 
the  bottom,  ill-defined  laterally,  marked  by  from  (J  to  10  plications  similar 
in  every  respecl  to  those  upon  the  lateral  slopes. 

Brachial  valve  less  convex  than  the  pedicle,  its  depth  usually  not  more 
than  one-hall'  that  of  the  pedicle  valve,  its  surface  is  gently  convex  across 
the  middle  portion,  hut  curves  ahruptly  to  the  lateral  margins  and  to  the 
cardinal  margin,  sometimes  a  little  compressed  towards  the  cardinal  ex- 
tremities; the  mesial  fold  is  depressed,  being  scarcely  elevated  above  the 
general  surface  of  the  valve  in  its  posterior  half,  it  is  rounded  in  contour 
and  ill-defined  laterally,  it  is  marked  by  plications  similar  in  form  and 
number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  are  not  preserved  in  the  casts,  but  the 
presence  of  concentric  lines  of  growth  art:  indicated  which  become 
crowded  near  the  anterior  margin 

Remarks. — This  species  has  been  observed  only  in  the  form  of  casts  in  a 
line-grained  yellow  sandstone.  If  may  be  distinguished  from  8.  sabrotundus, 
the  species  which  it  most  closely  resembles,  by  its  more  elongate  form. 
its  shallower  fold  and  sinus,  its  flatter  plications,  and  by  the  lateral 
compression  of  the  shell.  The  surfaces  of  the  lateral  slopes  of  the  two 
valves  of  8.  subrotundus  meet  at  the  lateral  margins  of  the  shell  in  an 
acute  angle  while  in  this  species  the  angle  is  at  most  obtuse  and  is  usually 
absent  because  of  the  inflection  of  the  lateral  margins  of  the  valves  to 
form  a  flattened  area  towards  the  cardinal  extremities.  The  peculiar 
elongate  form  of  the  species,  with  its  completely  plicated  shell  and  shal- 
low fold  and  sinus,  resembles  in  some  degree  the  elongate,  short-hinged 
varieties  of  the  Devonian  species,  S.  hungerfordi.  The  species  also  resem- 
bles in  its  elongate  form  and  general  proportions,  the  Russian  species  S. 
mosquensis  Pisch.,  but  does  not  grow  so  large  as  that  species.  The  re- 
lationships of  neither  this  species  nor  8.  svJbrotundus  with  the  completely 
plicated  Spirifers  of  the  8.  striatus  type,  represented  in  American  faunas 
by  8.  grimesi  and  8.  logcmi,  can  lie  determined,  since  the  minute  longi- 
tudinal stria'  of  those  species  cannot  be  detected  on  specimens  preserved 
as  these  are. 

Were  the  shell  itself  preserved  in  this  species,  it  is  not  improbable  that 
a  larger  number  of  plications  would  be  shown ;  in  the  condition  of  preser- 
vation of  the  specimens  about  50  plications  can  usually  be  detected  about  the 
margin  of  the  shell,  including  those  on  the  sides  and  in  the  fold  and  sinus, 
they  grow  faint  and  disappear  before  reaching  the  cardinal  extremities. 
and  on  the  shell  surface  itself  as  many  as  ten  or  more  additional  ones 
would  probably  be  seen. 

Horizon. — English  River  grit  of  the  Kinderhook. 


SPIRIFER  359 

,  Spirifer  gregeri  11.  sp. 

Plate  LV,  Figs.  1-8 

Description. — Shell  above  medium  size  or  rather  large,  usually  a  little 
longer  than  wide  but  sometimes  wider  than  long,  the  hinge-line  shorter 
than  the  greatest  width,  the  lateral  margins  usually  slightly  sinuate  just 
in  front  of  the  obtusely  angular  cardinal  extremities.  The  dimensions  of 
a  nearly  complete  pedicle  valve,  a  partial  internal  cast,  are:  length  55 
mm.,  greatest  widtli  53  mm.,  length  of  hinge-line  38  mm.,  convexity  22 
mm.,  height  of  cardinal  area  6  mm. 

Pedicle  valve  subhemispherieal,  the  greatest  depth  near  the  middle,  the 
surface  curving  rather  abruptly  in  all  directions  from  the  center  of  the 
valve,  becoming  very  slightly  compressed  towards  the  cardinal  extremi- 
ties ;  beak  small,  rather  strongly  incurved ;  the  cardinal  area  of  moderate 
height,  concave,  the  curvature  increasing  towards  the  beak,  the  lateral 
margins  sharply  denned,  sloping  gradually  from  the  beak  nearly  to  the 
cardinal  extremities,  where  they  bend  abruptly  to  the  hinge-line,  truncat- 
ing the  lateral  extremities  of  the  area;  mesial  sinus  inconspicuous  at  the 
beak,  becoming  more  pronounced  anteriorly,  it  is  usually  narrow  and  of 
moderate  depth,  rounded  in  the  bottom  and  not  sharply  defined  laterally, 
sometimes  scarcely  more  than  a  mesial  flattening  of  the  valve;  the  entire 
surface  of  the  valve,  both  the  lateral  slopes  and  the  mesial  sinus,  marked 
by  depressed  rounded  plications  which  bifurcate  frequently,  they  vary  in 
width  from  less  than  one  to  one  and  one-half  millimeters,  from  25  to  30 
or  more  occupy  each  lateral  slope  and  about  12  the  mesial  sinus. 

Brachial  valve  with  the  convexity  about  equal  to  the  pedicle,  the  great- 
est depth  posterior  to  the  middle,  the  surface  curving  rather  abruptly  to 
the  cardinal  margin  and  more  gently  to  the  lateral  and  anterior  margins, 
slightly  compressed  towards  the  cardinal  extremities;  the  cardinal  area 
narrow;  the  beak  obtusely  pointed  and  moderately  incurved;  the  mesial 
fold  inconspicuous  in  the  posterior  half  of  the  valve,  becoming  moderately 
elevated  anteriorly,  not  sharply  defined  laterally;  the  surface  of  the  valve 
marked  by  plications  entirely  similar  in  form  and  number  to  those  of  the 
opposite  valve. 

The  minute  surface  markings  of  both  valves  consist  of  extremely  fine 
radiating  stria2  which  are  often  entirely  obliterated  in  fossilization.  Con- 
centric lines  of  growth  are  present  which  are  unevenly  distributed  and 
vary  in  strengt  li. 

Remarks.— This  species  resembles  S.  grimesi  in  some  respects,  but  it  is 
a  smaller  shell  with  much  more  rotund  form,  especially  with  a  much  more 
conspicuously  subhemispherieal  pedicle  valve  and  a  narrower  mesial 
sinus. 

Horizon. — Lower  Burlington  limestone. 


360  MississilMMAN    BRACHIOPODA 

SPIRIFBB  ROWLEY1  Q.  sp. 

Plate  LI  1 1.  Figs.  3-6;  Plate  LigV,  Figs.  1-4 

1909.     Spirifer  grimesi  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  304,  pi.  13, 
figs.  1-2. 

Description.  Shell  large,  broader  than  long,  transversely  subelliptical 
in  outline,  the  hinge-line  shorter  than  the  greatest  width,  the  cardinal  ex- 
tremities subjugular  or  rounded.  The  dimensions  of  a  nearly  complete 
but  somewhat  distorted  specimen  are :  length  of  pedicle  valve  about  55 
mm.,  length  of  brachial  valve  about  47  mm.,  greatest  width  about  75  mm., 
length  of  hinge-line  about  55  mm.,  thickness  -f-32  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  depth  posterior  to 
the  middle,  the  umbonal  region  narrow,  the  surface  curving  abruptly  to 
the  cardinal  margin  each  side  of  the  beak,  becoming  somewhat  compressed 
towards  the  cardinal  extremities,  curving  more  gently  to  the  lateral  and 
anterior  margins;  the  beak  very  small  and  strongly  incurved;  cardinal 
ana  of  moderate  height,  nearly  flat  towards  the  cardinal  margin  but  be- 
coming rather  strongly  concave  towards  the  beak,  the  lateral  margins 
sharply  defined,  subparallel  with  the  cardinal  margin  for  the  greater  part 
of  their  length;  mesial  sinus  originating  as  a  narrow  and  sharply  defined 
furrow  at  the  beak,  becoming  broader,  less  sharply  defined  and  rather 
deep  anteriorly  where  it  is  rounded  in  the  bottom  and  somewhat  produced 
as  a  rounded  anterior  extension  of  the  valve ;  lateral  slopes  and  sinus 
marked  by  depressed,  rounded,  radiating  plications  which  bifurcate  fre- 
quently, they  are  from  one  to  two  millimeters  in  width,  from  25  to  30 
occupying  each  lateral  slope,  and  20  or  more  the  mesial  sinus  at  the  front 
margin. 

Brachial  valve  subelliptical  in  outline,  a  little  less  convex  than  the 
pedicle,  its  greatest  depth  near  the  middle,  the  surface  compressed  to- 
wards the  cardinal  extremities ;  the  cardinal  area  very  narrow  and  linear ; 
the  mesial  fold  well  defined  to  the  beak,  scarcely  elevated  above  the  gen- 
eral surface  in  the  umbonal  region,  becoming  strongly  elevated  in  front 
and  sometimes  slightly  recurved,  its  lateral  boundaries  less  sharply  de- 
fined anteriorly  than  towards  the  beak ;  the  entire  surface  of  the  valve 
marked  by  flattened,  bifurcating  plications  entirely  similar  in  form  and 
number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  exceedingly  fine  radiating 
stria?,  twenty  of  which  sometimes  occupy  the  width  of  a  single  plication. 

Remarks. — This  species  has  been  identified  commonly  as  8.  grimesi,  but 
it  may  be  easily  distinguished  from  that  species  by  its  narrower  umbonal 
region  and  more  pointed  beak,  and  by  the  narrower,  deeper  and  more 
sharply  defined  mesial  sinus.    The  minute  radiating  stria?  are  also  usually 


SPIRIPER  361 

more  conspicuous  upon  members  of  this  species,  although  this  may  he  due 
to  the  difference  in  preservation. 

Horizon. — Fern  Glen  formation  and  lower  Burlington  limestone. 

Spipjfer  gkimesi  Hall 
Plate  LI,  Figs.  1-2;  Plate  LIL  Figs.  1-4;  Plate  LIU,  Figs.  1-2. 

1858.     Spirifer  grimesi  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  604,  pi.  14,  figs.  1-5. 
1883.     Spirifera  Grimesi  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi.  (31)  56, 
figs.  8,  16-19. 

1894.  Spirifera  grimesi  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  79. 

1895.  Spirifer  Grimesi  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  30, 

figs.  8,  16-19. 

Description.  —  Shell  large,  varying  from  longitudinally  to  transversely 
subelliptical  in  outline,  the  length  sometimes  greater  but  usually  less  than 
the  width,  the  hinge-line  shorter  than  the  greatest  width,  the  cardinal 
extremities  rounded  or  obtusely  angular.  The  dimensions  of  two  indi- 
viduals, the  smaller  one  the  type  of  the  species,  are :  length  88  mm.  and 
85  mm.,  width  100  mm.  and  77  mm.,  thickness  61  mm.  and  53  mm.,  length 
of  hinge-line  80  mm.  and  52  mm.,  height  of  cardinal  area  8  mm  and  8  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  sloping  abruptly  from  the  rather  broad  umbonal 
region  to  the  cardinal  margin,  and  more  gently  to  the  antero-lateral 
margins,  sometimes  a  little  compressed  towards  the  cardinal  extremities ; 
beak  rather  obtusely  pointed  and  incurved  ;  cardinal  area  of  moderate 
height,  arched,  the  curvature  becoming  stronger  towards  the  beak,  some- 
times almost  flat  towards  the  hinge-line,  the  lateral  margins  very  sharply 
defined,  sloping  from  the  beak  to  the  cardinal  extremities,  the  slope 
becoming  more  abrupt  distally,  the  delthyrium  large,  broader  than  high ; 
lateral  slopes  convex,  becoming  more  or  less  flattened  towards  the  cardinal 
extremities,  covered  with  depressed,  rounded,  bifurcating  plications; 
mesial  sinus  rather  broad  and  shallow,  usually  rounded  but  sometimes 
somewhat  angular  in  the  bottom,  originating  near  the  beak  where  it  is 
rather  sharply  defined  when  the  surface  of  the  shell  has  not  been  eroded, 
loosing  its  definition  anteriorly,  sometimes  produced  in  front  into  a 
nasute  or  lingual  extension,  its  surface  covered  with  bifurcating  plica- 
tions like  those  on  the  lateral  slopes. 

Brachial  valve  about  as  convex  as  the  pedicle,  the  greatest  convexity 
near  the  middle ;  the  lateral  slopes  convex,  becoming  somewhat  com- 
pressed towards  the.  cardinal  extremities,  marked  by  depressed,  rounded 
plications  like  those  of  the  opposite  valve ;  the  mesial  fold  broad,  rounded, 
ill-defined,  sometimes  becoming  strongly  elevated  and  somewhat  angular 
towards  the  front,  originating  at  the  beak  where  it  is  scarcely  or  not 
at  all  elevated  above  the  general  surface  of  the  valve,  marked  with  plica- 
tions like  those  upon  the  lateral  slopes  of  the  shell. 


362 


MISSISSIPPIAN    BHACIIIOI'ODA 


Surface  of  each  valve  marked  by  80  or  more  depressed,  rounded,  bifur- 
cating plications,  aboul  20  to  25  of  which  occupy  the  fold  and  sinus. 
The  minute  surface  markings  consist  of  exceedingly  fine  radiating  stria?, 
about  (i  in  lo  of  which  occupy  each  plication,  and  by  still  finer  concentric 
striaa  which  give  to  the  surface  of  perfectly  preserved  shells  a  finely  can- 
cellated ornamentation.  Concentric  lines  of  growth  are  usually  dis- 
tributed over  the  surface  of  the  shell  in  an  irregular  manner,  often 
becoming  somewhal  crowded  anteriorly. 

Internally  the  muscular  impressions  in  the  pedicle  valve  are  strongly 
impressed,  the  muscular  area  is  mors  or  less  rhombic  in  outline  but  varies 
greatly  in  proportionate  width,  in  some  individuals  being  twice  as 
wide  iis  in  other  shells  of  approximately  the  same  size.  The  dental 
lamelhe  are  short  and  more  or  less  widely  divergent,  the  divergence  de- 
pendent upon  the  width  of  the  muscular  area  :  between  the  dental  lamelhe 

towards  the  beak,  at  least  in  old  individuals,  there  is  a  secretion  of  cal- 
careous matter  which  completely  solidities  the  shell  in  that  region,  this 
solidification,   however,   does   not    extend   out    to   the   plane  of  the   surface 

of  the  cardinal  area,  its  posterior  surface  appearing  as  a  transverse  area 
with  a  median  keel  or  ridge,  somewhat  deeply  depressed  in  the  upper 
part  of  the  delthyrium,  its  lower  margin  being  angularly  notched. 

Remarks. — This  species  is  one  of  the  most  common  and  characteristic 
fossils  of  the  Burlington  limestone,  but  it  usually  occurs  in  a  more  or 
less  fragmentary  condition.  Specimens  preserving  both  valves  are  ex- 
ceedingly rare,  the  most  common  examples  being  specimens  of  the  pedicle 
valve  which  are  more  or  less  incomplete  about  the  margin.  The  nearest 
relative  of  »S'.  grimesi  in  the  faunas  of  the  Mississippi  valley  is  S.  logon/ 
of  the  Keokuk  limestone,  and  in  the  fragmentary  condition  in  which 
both  species  are  usually  preserved  it  is  often  difficult  to  properly  dis- 
tinguish between  them.  With  complete  or  fairly  complete  examples  of  the 
two  species,  it  is  seen  that  S.  grimesi  is  characterized  by  the  shorter  hinge- 
line,  rounded  cardinal  extremities,  and  proportionally  more  elongate 
shell.  The  elongation  of  the  shell  is  a  variable  character  in  the  species 
as  is  indicated  by  the  measurements  of  the  two  examples  given  above, 
the  type  specimen  being  an  extreme  form  in  which  the  length  is  greater 
than  the  width,  the  more  usual  condition  is  shown  by  the  measurements 
of  the  larger  individual  having  the  width  greater  than  the  length.  From 
the  characters  mentioned,  especially  the  proportionate  length  of  the 
hinge-line,  it  is  not  infrequently  possible  to  identify  the  incomplete  ex- 
amples of  the  species  as  they  usually  occur,  since  one  or  more  lines  of 
growth  can  usually  be  detected.  If  these  lines  converge  as  they  approach 
the  cardinal  margin  the  species  is  clearly  a  member  of  the  species  8. 
grimesi,  but  if  they  diverge  it  is  S.  logani. 

Horizon. — Burlington  limestone. 


SPIRIFER  363 

Spirifer  logani  Hall 

Plate  LV1.  Figs.  1-3;  Plate  LVII,  Figs.  1-3 

1858.     Spirifer  logani  Hall,  Geol.  Iowa.  vol.  1,  pt.  2,  p.  647,  pi.  '20,  fig.  7; 

pl.  21.  tigs,  la-b,  2. 
1863.     Spirifer  Icevigatus  Swallow.   Trans.   St.   Louis   Acad.   Sci..   vol.   2, 

p.  Sfi. 
1883.     Spirifera  Logani  Hall,  Rep.  X.  Y.  State  Geol.  for  1882,  pl.  (32)  57, 

figs.  7,  8. 
1894.     Spirifer  Logani  Hall  and  Clarke,  Int.  to  Studv  of  Brach.,  pt.  2, 

pl.  26,  fig.'  10. 
1894.     Spirifera  lo</<tni  Keyes,  Mo.  Geol.  Surv..  vol.  5,  p.  81. 
IS!).").     Spirifer  Logani  Hall  and  Clarke,   Pal.  N.  Y.,  vol.  8,  pt.  2,  pl.  32, 

figs.  7,  8. 

Description.  —  Shell  large,  wider  than  long,  the  greatest  width  along  the 
hinge-line,  the  cardinal  extremities  usually  acutely  angular  or  acuminate, 
sometimes  rectangular.  The  dimensions  of  two  individuals  are:  length 
80  mm.  and  61  mm.,  width  120  mm.  and  88  mm.,  thickness  53  mm.  and  40 
mm.,  height  of  cardinal  area  9.5  mm.  and  9  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  sloping  abruptly  from  the  broad  umbonal  region 
to  the  cardinal  margin,  and  rather  gently  to  the  lateral  and  anterior 
margins,  distinctly  flattened  towards  the  cardinal  extremities;  beak 
rather  obtusely  pointed  and  incurved;  cardinal  area  of  moderate  height, 
arched,  the  curvature  becoming  stronger  towards  the  beak,  sometimes 
nearly  or  quite  flat  towards  the  hinge-line,  the  lateral  margins  sharply 
defined,  sometimes  nearly  parallel  with  the  hinge-line  through  the  greater 
part  of  the  length  and  then  sloping  abruptly  to  the  cardinal  extremities, 
in  other  specimens  sloping  somewhat  gradually  from  the  beak  to  the 
cardinal  extremities;  the  delthyrium  large,  broadly  triangular,  some- 
times twice  as  wide  at  its  base  as  the  total  height;  lateral  slopes  convex 
towards  the  median  part  of  the  valve,  becoming  concave  towards  the 
cardinal  extremities,  covered  with  depressed,  rounded,  bifurcating  plica- 
tions from  1  to  2  mm.  in  width;  mesial  sinus  broad  and  usually  rather 
shallow,  rounded  in  the  bottom,  originating  near  the  beak,  its  lateral 
boundaries  indefinitely  marked,  produced  into  a  nasute  extension  anter- 
iorly, its  surface  covered  with  bifurcating  plications  similar  to  those 
upon  the  sides  of  the  shell. 

Brachial  valve  about  as  convex  as  the  pedicle,  its  greatest  convexity 
near  the  middle;  the  lateral  slopes  convex  towards  the  middle  part  of 
the  shell,  becoming  concave  or  flattened  towards  the  cardinal  extremi- 
ties, marked  by  depressed,  rounded,  bifurcating  plications  like  those  on 
the  opposite  valve;  mesial  fold  broad,  rounded,  ill-defined,  sometimes 
becoming  strongly   elevated  towards  the   front   and   somewhat   angular, 


364 


MISSISS1PPIAN    BRACHIOPOD.A 


originating  at  the  beak  where  it  is  scarcely  or  ool  a1  ;i!l  elevated  above 
the  genera]  surface  of  the  valve,  marked  by  plications  similar  to  those 
upon  the  Lateral  slopes  of  the  valve. 

Surface    of   each    valve    marked    by    SO     or     more     depressed,    rounded, 

bifurcating  plications,  about  20  to  25  of  which  occupy  the  fold  and 
sinus.  The  minute  surface  markings  consist  of  exceedingly  fine  radiating 
striae,  about  (>  to  10  of  winch  occupy  each  plication,  and  by  still  finer 
concentric  stria'  which  give  to  the  surface  of  perfectly  preserved  shells 
a  finely  cancellated  ornamentation.  Concentric  lines  of  growth  are 
usually  distributed  over  the  surface  of  the  shell  in  an  irregular  manner, 
often  becoming  somewhat  crowded  anteriorly. 

Remarks. — This  species  has  its  nearest  ally  in  the  Mississippi  basin  in 
»■>.  grimesi,  these  two  Spirifers  being  the  largest  members  of  the  genus 
in  America.  In  their  surface  ornamentation  the  two  species  are  essen- 
tially identical,  the  distinction  between  them  being  found  in  the  greater 
length  of  the  hinge-line  in  S.  logaui  and  in  its  proportionally  broader  shell. 
In  their  internal  characters  the  two  species  are  also  essentially  alike, 
although  the  muscular  impressions  in  the  pedicle  valve  of  8.  logani  are 
sometimes  proportionally  broader  and  shorter.  In  their  stratigraphic 
relations  S.  logani  is  characteristic  of  the  Keokuk  limestone,  while  S. 
grimesi  is  a  member  of  the  next  older  fauna  of  the  Burlington  limestone. 

Horizon.  —  Keokuk    limestone. 


Spirifer  striatiformis  Meek 
Plate  XLVIII,  Figs.  17-21 

1875.     Spirifer  (Trigonotnta)  striatiformis  Meek,  Pal.  Ohio,  vol.  2,  p.  289, 

pi.  14,  figs.  8a-e. 
1888.     Spirifer  striatiformis  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3, 

p.  44,  pi.  1,  fig.  6;  pi.  3,  figs.  23-26;  pi.  6,  figs.  6,  7;  pi.  12,  fig.  20. 
1888.     Spirifer  striatiformis  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  4, 

pi.  2,  fig.  9. 
1895.     Spirifer  striatiformis  Herrick,  Geol.  Surv.  Ohio,  vol.  7,  pi.  15,  fig.  9. 

Description.  —  Shell  of  medium  size,  wider  than  long,  the  greatest  wdth 
at  or  near  the  hinge-line,  the  lateral  margins  usually  meeting  the  hinge- 
line  in  nearly  a  right  angle  and  rounding  to  the  front,  the  anterior 
margin  rounding,  usuall\r  projecting  a  little  in  the  middle.  The  dimen- 
sions of  a  nearly  perfect  specimen  are :  length  of  pedicle  valve  35  mm., 
length  of  brachial  valve  28  mm.,  width  ±46  mm.,  thickness  25  mm.,  height 
of  cardinal  area  5  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  umbonal  region  rather  broad,  the  surface  curving 
rather  abruptly  to  the  cardinal  margins  for  a  short  distance  on  each  side 
of  the  beak,  curving  more  gently  to  the  antero-lateral  margins,  somewhat 


SP1RIFEE  365 

compressed  towards  the  cardinal  extremities,  wit  li  ;i  more  or  less  ill-defined 
sinuosity  passing  obliquely  from  each  side  of  the  beak  to  the  lateral 
margins  just  in  front  of  the  cardinal  extremities;  beak  small,  acuminately 
pointed,  strongly  incurved;  cardinal  area  of  medium  height,  arched  and 
sloping  posteriorly,  the  curvature  becoming  greater  towards  the  beak, 
the  lateral  margins  sharply  defined,  sloping  from  the  beak  to  the  cardinal 
extremities  in  a  convex  curve  which  becomes  more  abrupt  distally ;  lateral 
slopes  each  marked  by  about  25  depressed,  rounded  plications  which 
bifurcate  more  or  less  frequently  anywhere  between  the  cardinal  and 
anterior  margins,  but  more  frequently  towards  the  beak,  these  plications 
grow  successively  smaller  towards  the  cardinal  extremities,  the  smaller 
ones  sometimes  becoming  very  faint  or  almost  obsolete;  mesial  sinus 
shallow,  narrow  and  sharply  denned  at  the  beak,  becoming  broad  and 
ill-defined  anteriorly,  marked  by  a  median  plication  which  originates 
near  the  beak  and  which  usually  divides  into  two  anteriorly,  on  each 
side  there  are  four  or  five  plications  which  originate  from  the  inner 
margins  of  the  bounding  plications  or  through  the  bifurcation  of  plica- 
tions so  originating,  making  10  to  12  plications  altogether  in  the  sinus 
which  are  similar  in  all  respects  to  those  of  the  lateral  slopes. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
or  posterior  to  the  middle,  the  surface  curving  rather  abruptly  from  the 
umbonal  region  to  the  cardinal  margin*  sloping  with  a  much  more  gentle 
curve  to  the  antero-lateral  margins,  somewhat  compressed  towards  the 
cardinal  extremities ;  mesial  fold  defined  to  the  beak,  depressed  and 
but  slightly  raised  above  the  general  surface  of  the  valve  posteriorly, 
becoming  more  elevated  and  rounded  anteriorly  but  less  sharply  defined ; 
marked  by  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve,  all  of  which  originate  through  the  division  of  a  single  one  at  the 
beak ;  lateral  slopes  marked  by  plications  similar  in  form  and  number  to 
those  of  the  opposite  valve. 

The  minute  surface  markings  consist  of  exceedingly  fine  longitudinal, 
rounded  corrugations  variable  in  width,  the  coarser  ones  generally  in 
the  furrows  between  the  plications,  from  8  to  12  occupying  the  space 
of  1  mm.,  crossing  these  are  minute  sublamellose  concentric  markings 
somewhat  further  apart  than  the  longitudinal  corrugations.  A  few 
concentric  lines  of  growth  are  present  at  irregular  intervals. 

Remarks. — This  species  was  originally  described  from  the  Waverly  of 
Ohio,  and  the  description  given  above  has  been  written  from  such  speci- 
mens. Other  specimens  from  the  Chouteau  limestone  in  Missouri  have 
been  identified  with  the  Ohio  shell,  although  none  have  been  seen  which 
are  so  complete  or  so  well  preserved  as  some  of  the  Ohio  examples.  So 
far  as  they  are  preserved  the  Chouteau  limestone  specimens  agree  closely 
in  almost  every  respect  with  the  authentic  examples  of  the  species,  they 


36G  MISSISSIPPIAN    BRACHIOPODA 

arc  similar  in  size  and  proportions  and  possess  the  same  form  of  minute 
radial  corrugations,  but  the  more  minute  concentric  markings  have  been 
almosl  obliterated  in  all  specimens  examined*  The  mesial  sinus  in  the 
pedicle  valve  of  the  Chouteau  limestone  examples  is  perhaps  slightly 
more  angular  than  in  the  Ohio  specimens,  hut  without  more  evidence 
this  character  is  not  of  enough  importance  to  justify  a  specific  differ- 
entiation. 

Horizon.  —  Waverly  group  and  Chouteau  limestone  of  the  Kinderhook 

Spirifer  mortonanus  Miller 
Plate  LVIII,  Figs,  1-3;  Plate  LIX,  Figs.  1-6 

L870.     Spirifer  f<isti<jnli<s  Meek  and  Worthen,  Proc.  Acad.  Nat.  Sci.  Phil., 

I>.  36.     (Not  8.  fastigatus  Morton,  1836.) 
1875.     Spirifer  fastigatus  Meek  and  Worthen,  Geol.  Surv.  111.,  vol.  6,  p.  521, 

Pl.  30,  lig.  3. 
1SS3.     Spirifera  mortonana  Miller,  Am.  Pal.  Foss.,  2nd  ed.,  p.  298. 
181)5.     Spirifi  r  Mortonanus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pl.  38, 

figs.   18,   19. 

Description.—  Shell  above  medium  size,  much  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  acutely  angular.  The 
dimensions  of  two  individuals  are:  length  39  mm.  and  34  mm.,  width  69 
mm.  and  63  mm.,  thickness  35  mm.  and  27.5  mm.,  height  of  cardinal  ana 
8  mm.  and  6  mm.     The  width  of  the  largest  specimen  observed  is  96  mm. 

Pedicle  valve  convex  in  the  middle  on  each  side  of  the  sinus,  the  curva- 
ture usually  becoming  a  little  more  abrupt  as  it  approaches  the  antero- 
lateral margins,  the  surface  becoming  compressed  or  concave  towards 
the  cardinal  extremities,  often  developing  a  more  or  less  distinct  oblique 
sinus  on  each  side  passing  from  near  the  beak  to  the  lateral  margins 
just  in  front  of  the  cardinal  extremities,  the  umbonal  region  rather  broad ; 
beak  small  and  pointed,  incurved ;  cardinal  area  rather  high,  arched, 
the  curvature  increasing  towards  the  beak,  the  inferior  portion  sloping 
posteriorly  at  an  angle  of  about  120  degrees  to  the  plane  of  the  valve, 
the  lateral  margins  sharply  defined,  extending  laterally  from  the  beak 
with  a  very  slight  slope,  being  sub-parallel  with  the  cardinal  margin 
nearly  to  the  end,  where  they  drop  off  abruptly  to  the  cardinal  extrem- 
ities; delthyrium  large,  wider  than  high,  the  surface  of  the  area  vertically 
striate  and  marked  by  faint,  longitudinal  lines  of  growth ;  lateral  slopes 
of  the  valve  each  marked  by  from  10  to  12  rounded  or  subangular  plica- 
tions near  the  beak  which  grow  gradually  smaller  towards  the  cardinal 
extremities,  beyond  them  a  considerable  area  of  the  shell  is  marked  by 
much  finer  plications,  6  or  8  of  which  can  be  detected  in  some  individuals, 
while  in  others  they  are  nearly  obsolete,  from  2  to  6  of  the  larger  plica- 
tions on   each  lateral  slope  divide  in  the  umbonal   region  and  continue 


SPIRIFEK 


367 


more  or  less  distinctly  in  pairs  to  the  anterior  margin  of  the  shell;  mesial 
sinus  subangular  or  somewhat  rounded  in  the  bottom,  defined  to  the 
beak,  often  produced  anteriorly  in  a  nasute  or  lingual  extension,  the 
plications  usually  somewhat  fainter  than  the  larger  ones  on  the  lateral 
slopes;  they  consist  of  a  median  one  winch  originates  near  the  beak  and 
passes  without  division  to  the  anterior  margin;  on  each  side  of  the  sinus 
there  are  two  or  three  Lateral  plications  which  are  given  off  serially  from 
the  inner  margins  of  the  bounding  plications. 

Brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  its 
greatest  convexity  near  or  in  front  of  the  middle;  mesial  fold  sub-angular 
or  sometimes  rounded,  well  defined  to  the  beak,  moderately  or  rather 
highly  elevated  anteriorly,  marked  by  a  median  furrow  corresponding  to 
the  median  plication  of  the  opposite  valve,  and  by  three  or  four  lateral 
plications,  all  of  which  join  to  form  a  single  one  at  the  beak;  lateral 
slopes  each  convex  towards  the  mesial  fold,  becoming  flattened  or  a 
little  concave  towards  the  cardinal  extremities,  marked  by  plications 
similar  in  form  ami  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  consist  of  fine  concentric  lines  which  are 
somewhat  irregular  in  the  strength  of  their  development,  and  by  occa- 
sional much  stronger  lines  of  growth. 

Internally  the  muscular  impressions  of  the  pedicle  valve  are  broadly 
ovate  and  deeply  impressed,  the  shell  in  the  umbonal  and  cardinal  regions 
being  much  thickened. 

Remarks. — This  species  is  especially  characteristic  of  the  Crawfords- 
ville  shale  of  Keokuk  age.  It  is  characterized  by  its  elongate  hinge-line 
which  in  young  individuals  is  distinctly  acuminate,  by  the  rather  broad 
area  of  the  pedicle  valve  with  subparallel  margins,  and  by  the  rather 
coarse,  dividing  plications. 

Horizon. — Keokuk  (Crawfordsville  beds  of  Indiana). 

Sl'IKIFER   MONTGOMERYENSIS   U.   sp. 

Plate  LV,  Fig.  9 

Description. — Shell  above  medium  size,  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  angular,  acuminate  in 
the  type  specimen.  The  dimensions  of  a  pedicle  valve  are:  length  37 
mm.,  width  75  mm.,  convexity  15.5  mm.,  height  of  cardinal  area  7  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  umbonal  region  broad,  the  surface  curving  abruptly  to 
the  cardinal  margin  for  a  short  distance  on  each  side  of  the  beak,  the 
curve  to  the  antero-lateral  margins  gentle,  somewhat  compressed  toward 
the  cardinal  extremities;  beak  small,  acuminate,  moderately  incurved; 
cardinal  area  gently  arched,  the  curvature  becoming  stronger  toward  the 
beak,  its  lateral  margins  sharply  defined,  sloping  gently  from  the  beak 


368  .Mississil-I'IAN    BBACHIOPODA 

distally,  the  slope  becoming  much  more  abrupt  as  it  approaches  the  car- 
dinal extremities]  delthyrium  large,  broader  than  high;  lateral  slopes 
with  a  more  or  less  distinct  sinuosity  extending  obliquely  from  each  side 
of  the  beak  to  the  lateral  margins  just  in  front  of  the  cardinal  extremi- 
ties, eaeh  marked  with  about  25  rounded  or  subangular  plications,  5  to  8 
of  which  towards  the  sinus  are  double,  with  about  10  additional  single 
ones  towards  the  cardinal  extremities,  the  last  3  or  4  of  which  are  but 
faintly  developed,  the  double  plications  bifurcate  in  the  umbonal  region 
and  continue  in  pairs  to  the  anterior  margin,  the  grooves  between  the 
pairs  being  distinctly  wider  and  deeper  than  these  between  the  two  pli- 
cations of  eacli  pair;  mesial  sinus  distinctly  defined  from  the  beak  to  the 
anterior  margin,  subangular  in  the  bottom,  marked  by  a  median  plication 
which  originates  near  the  beak  and  continues  without  division  to  the  an- 
terior margin,  on  each  side  of  the  sinus  there  are  3  or  4  plications  which 
originate  from  the  inner  margin  of  the  bounding  plications  or  from  the 
hi  furcation  of  such  plications. 

Brachial  valve  not  observed. 

The  surface  markings  of  the  shell  consist  of  fine,  sublamellose,  concen- 
tric lines  which  are  crowded  at  intervals  to  form  more  or  less  conspicuous 
lines  of  growth. 

Remarks.— This  species  is  more  closely  allied  to  8.  mortonensis  than  to 
any  other,  but  it  may  be  easily  separated  from  that  species  by  means  of 
the  distinctly  duplicate  plications  which  occupy  a  considerable  area  on 
each  side  of  the  sinus,  and  by  the  more  sharply  denned  mesial  sinus  of 
the  pedicle  valve. 

Horizon. — Keokuk  (Harrodsburg  limestone  of  Indiana). 

Spirifer  calvini  n.  sp. 
Plate  LIV,  Figs.  5-10 

Description. — Shell  of  medium  size,  wider  than  long,  the  greatest  width 
at  or  near  the  hinge-line,  the  cardinal  extremities  angular  or  a  little 
rounded.  The  dimensions  of  a  nearly  complete  individual,  slightly  dis- 
torted in  such  a  manner  as  to  reduce  the  length  and  increase  the  thickness, 
are:  length  of  pedicle  valve  29  mm.,  length  of  brachial  valve  24.5  mm., 
width  45.5  mm.,  thickness  30.5  mm.,  height  of  cardinal  area  8  mm. 

Pedicle  valve  subpyradimal  in  form,  the  umbo  prominent ;  beak  pointed, 
more  or  less  incurved,  sometimes  a  little  twisted ;  cardinal  area  high,  con- 
cave, marked  by  longitudinal  lines  of  growth,  the  lateral  margins  defined 
but  sometimes  curving  rather  abruptly  into  the  lateral  slopes,  sloping 
from  the  beak  to  the  cardinal  extremities  in  a  slightly  convex  curve,  the 
delthyrium  large,  broadly  triangular;  lateral  slopes  convex,  sloping 
steeply  from  the  umbonal  region  to  the  antero-lateral  margins,  each 
marked  by  from  12  to  14  simple,  depressed  convex,  plications  which  are 


SPIRIFER  369 

separated  by  grooves  narrower  than  the  plications  themselves;  mesial 
sinus  rather  shallow  or  of  moderate  depth,  flattened  or  rounded  in  the 
bottom,  rather  sharply  defined  at  the  beak  hut  becoming  ill-defined  ante- 
riorly, marked  by  4  or  5  much  flattened  plications  separated  by  narrow 
grooves. 

Brachial  valve  shallower  than  the  pedicle,  with  a  narrow  cardinal 
area;  mesial  fold  depressed  convex,  sharply  defined  but  scarcely  elevated 
in  the  umbonal  region,  becoming  moderately  elevated  towards  the  front, 
marked  by  much  flattened  plications  similar  in  form  and  number  to  those 
of  the  sinus  of  the  opposite  valve ;  lateral  slopes  most  convex  towards  the 
center  of  the  valve,  usually  becoming  a  little  compressed  towards  the 
cardinal  extremities,  the  surface  curving  abruptly  from  the  umbonal  re- 
gion to  the  cardinal  margin,  the  slope  more  gentle  to  the  antero-lateral 
margins,  marked  by  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve. 

The  minute  surface  markings  consist  of  fine  granules  which  are  some- 
what elongate  longitudinally.  Rather  fine  concentric  lines  of  growth  are 
also  present  which  are  crowded  at  intervals,  especially  towards  the  front, 
to  form  stronger  growth  lines. 

Remarks.— -The  fine  surface  markings  of  this  species  are  usually  de- 
stroyed through  the  exfoliation  of  the  shell.  The  species  is  quite  unlike 
any  other  Mississippian  species  of  the  genus,  being  especially  character- 
ized by  the  elevated  beak,  the  high  cardinal  area,  and  the  much  flattened 
plications  of  the  fold  and  sinus,  these  plications  being  much  more  de- 
pressed than  those  upon  the  lateral  slopes  of  the  shell. 

Horizon.- — Kinderhook. 

Spirifer  jeffersonensis  Weller 

Plate  XLII,  Figs  17-21 

1906.     Spirifer  jeffersonensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  16, 
p.  444.  pi.  6,  figs.  18-22. 

Description.— -Shell  below  medium  size,  wider  than  long,  the  hinge-line  a 
little  shorter  than  the  greatest  width,  the  cardinal  extremities  rounded. 
The  dimensions  of  a  nearly  complete  pedicle  valve  are:  length  18  mm., 
greatest  width  22.5  mm.,  length  of  hinge-line  21.5  mm.,  height  of  cardinal 
area  7  mm.,  convexity  11  mm.  The  dimensions  of  a  brachial  valve  are: 
length  15  mm.,  width  22  mm.,  convexity  6  mm. 

Pedicle  valve  strongly  convex  with  the  greatest  depth  towards  the  um- 
bonal region,  the  surface  curving  gently  from  the  umbo  to  the  anterior 
and  antero-lateral  margins  and  more  abruptly  to  the  cardinal  margin, 
scarcely  compressed  towards  the  cardinal  extremities ;  the  beak  obtusely 
pointed   and   incurved;  cardinal   area  high,  concave,  with   the   curvature 


370 


M  ISSISSII'I'lAN    HHACIllOl'ODA 


increasing  towards  the  beak,  the  Lateral  margins  not  sharply  defined,  the 
surface  of  the  area  rounding  into  the  surface  of  the  lateral  slopes;  the 
delthyrium  Large  and  broadly  triangular;  the  mesial  sinus  of  moderate 
depth,  rounded  in  the  bottom,  well  defined  laterally  and  continuing    to 

the  beak,  il  is  marked  by  two  more  or  less  indistinct,  sometimes  nearly 
obsolete  plications;  lateral  slopes  each  marked  by  from  8  to  12,  usually 
9  or  10  simple,  rounded  plications. 

Brachial  valve  subelliptical  in  outline,  moderately  convex,  Ihe  greatest 
depth  posterior  to  the  middle,  the  surface  curving  abruptly  to  the  car- 
dinal margin  and  more  gently  to  the  anterior  and  anlero-lateral  margins, 
\ei-y  slightly  or  not  at  all  compressed  towards  the  cardinal  extremities; 
mesial  i'old  sharply  defined  to  the  beak  but  scarcely  elevated  above  the 
general  surface  in  the  posterior  halt'  of  the  valve,  becoming  moderately 
elevated  anteriorly,  it  is  marked  by  three  or  four,  low,  rounded,  indis- 
tinct plications  which  often  appear  to  be  almost  obsolete;  the  lateral 
slopes  marked  by  simple,  rounded  plications  entirely  similar  in  form  and 
number  to  those  of  the  opposite  valve. 

The  finer  surface  markings  consist  of  minute  concentric  lines  of 
growth,  which  are  usually  nearly  or  quite  destroyed  by  the  exfoliation  of 
the  shell. 

Remarks.- — In  its  high  cardinal  area  and  inconspicuous  plications  on 
the  fold  and  sinus  this  species  suggests  the  genus  Syringothyris,  but  it  lacks 
the  syrinx  and  the  punctate  shell  structure  of  that  genus.  At  one  time 
it  was  believed  that  certain  specimens  in  Ihe  Bushberg  sandstone,  in 
which  the  presence  of  a  syrinx  is  clearly  shown,  were  examples  of  this 
species,  and  that  the  species  should  therefore  be  transferred  to  Syringothy- 
ris,1 but  later  observations  have  demonstrated  that  the  two  forms  are  not 
the  same,  and  that  this  species  is  a  true  Spirifer  and  the  olher  a  genuine 
Syringotliy  ris. 

Horizon. — Glen  Park  limestone  of  the  Kindcrhook. 


Genus  BRACHYTHYRIS  McCoy 

Description. — Shells  varying  in  size  from  small  to  large,  the  length  and 
width  subequal,  the  outline  ovate  to  subcircular;  the  hinge-line  straight, 
much  shorter  than  the  greatest  width  of  the  shell,  the  cardinal  extremi- 
ties rounded.  Mesial  sinus  of  the  pedicle  valve  and  the  fold  of  the 
brachial  valve  more  or  less  well  developed.  Surface  of  both  valves 
marked  by  radiating  plications  which  are  simple  upon  the  lateral  slopes 
of  the  valves,  those  of  the  fold  and  sinus  increasing  in  number  in  passing 
from  the  beak  to  the  front  margin.  The  pedicle  valve  with  the  beak 
usually  only  moderately  elevated  above  the  hinge-line,  and  the  cardinal 
area   rather  strongly  arched.     Internally,  the  dental   lamella'  supporting 

i  Jour.  Geol.,  vol.  17,  p.  272.     (1909.) 


BRACHYTHYRIS  371 

the  hinge-teeth  are  short,  commonly  being  only  ridge-like  thickenings  of 
the  inner  surface  of  the  valve  on  each  side  of  the  delthyrium.  the  muscu- 
lar scars  ill-defined.  The  brachial  valve  commonly  less  convex  than  the 
pedicle,  with  a  very  narrow,  inconspicuous  cardinal  area,  the  cardinal 
process  low,  with  its  anterior  surface  vertically  striated;  the  form  of  the 
brachidiuml  as  in  Spirifer. 

Remarks.— The  genus  Brachythyris  was  proposed  by  McCoy  in  1862,  for 
the  ovate,  short-hinged  Spirifers  of  which  8.  ovalis  Phill.  was  figured  as  a 
typical  form,  and  which  must  be  assumed  as  the  genotype,  as  has  been 
pointed  out  by  Buckman.1  The  shells  of  this  type  constitute  a  well  de- 
fined group  of  species  which  may  be  conveniently  separated  from  Spirifer 
proper,  although  it  has  usually  been  the  custom  to  consider  the  name  as 
strictly  synonymous  with  Spirifer.  In  the  American  Mississippian  faunas 
Spirifer  suborbicularis  is  a  typical  member  of  the  genus. 

Brachythyris  burlingtonensis  n.  sp. 

Plate  LIII,  Figs.  8-9;  Plate  LXXXIII,  Pig.  6 

1901.     Spirifer  peculiaris    ?  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
p.  165.  pi.  14.  figs.  6-9. 

Description.  —  Shell  small,  longitudinally  semielliptical  in  outline,  the 
hinge-line  usually  a  little  shorter  than  the  greatest  width  of  the  shell,  the 
greatest  width  posterior  to  the  middle,  the  cardinal  extremities  usually 
rounded.  The  dimensions  of  a  small,  nearly  complete  internal  cast,  are : 
length  of  pedicle  valve  11.5  mm.,  length  of  brachial  valve  11  mm.,  great- 
est width  13.3  mm.,  length  of  hinge-line  10  mm.,  thickness  9  mm.,  height 
of  cardinal  area  2  mm.  The  dimensions  of  a  larger  pedicle  valve  are : 
length  19.5  mm.,  greatest  width  18  mm.,  length  of  hinge-line  13  mm.,  con- 
vexity 8  mm.,  height  of  cardinal  area  2.5  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbo  prominent,  the  surface  curving  abruptly  to  the  cardinal 
margin  and  more  gently  to  the  antero-lateral  margins,  slightly  or  not  at 
all  compressed  towards  the  cardinal  extremities;  beak  small,  pointed,  in- 
curved ;  cardinal  area  small,  arched,  the  curvature  increasing  towards 
the  beak,  lateral  margins  sloping  from  the  beak  to  the  cardinal  extremi- 
ties, scarcely  defined,  the  surface  of  the  area  curving  with  little  or  no 
demarcation  into  the  lateral  slopes  of  the  valve;  lateral  slopes  convex, 
marked  by  from  8  to  10  simple,  rounded,  depressed  plications  which  grow 
fainter  towards  the  cardinal  extremities;  mesial  sinus  narrow,  shallow, 
flattened  in  the  bottom,  sometimes  but  little  more  than  a  flattening  of 
the  valve  along  its  median  line,  bounded  by  a  pair  of  plications  which  are 
notably  broader  and  stronger  than  those  of  the  lateral  slopes,  smooth  in 

i  Science,  new  ser.,  vol.  26,  p.  379.     (1907.) 


'.)  i'J,  MISS1SSIPPIAN    BRAOHIOPODA 

the  smaller  individuals  hut  in  the  Larger  ones  marked  by  a  more  or  Less 
obscure  median  plication  which  originates  near  the  middle  of  the  valve. 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexily  pos- 
terior to  the  middle,  the  surface  curving  abruptly  to  the  cardinal  margin, 
sloping  with  a  gentle  convex  curvature  to  the  antero-lateral  margins,  a 
little  compressed  towards  the  cardinal  extremities;  mesial  fold  narrow, 
defined  to  the  beak,  rounded,  barely  elevated  above  the  general  surface 
of  the  valve,  smooth  in  all  of  the  examples  observed;  lateral  slopes 
marked  by  plications  similar  in  form  and  number  to  those  of  the  opposite 
valve. 

The  minute  surface  markings  of  the  shell  are  not  shown  on  any  of 
the  specimens  observed  because  of  their  condition  of  preservation,  but  a 
few  concentric  lines  of  growth  are  usually  recognizable. 

lit  murks. — This  species  has  only  been  observed  in  the  form  of  internal 
casts  and  natural  moulds  of  the  exterior,  in  a  fine-grained  sandstone.  In 
the  internal  casts  the  beak  of  the  pedicle  valve  is  always  obtuse  and  more 
or  less  truncated,  indicating  a  notable  thickening  of  the  shell  in  that  re- 
gion. A  few  natural  moulds  of  the  exterior  have  been  observed,  from 
which  artificial  casts  of  the  beak  and  cardinal  area  have  been  secured, 
which  show  the  external  form  of  that  portion  of  the  shell.  In  the  dimen- 
sions of  the  small,  complete,  internal  cast  given  above,  the  length  of  the 
pedicle  valve  is  materially  less  than  it  would  be  were  the  shell  itself  pre- 
served. The  total  length  of  the  other  specimen  whose  dimensions  are 
given  is  estimated  from  a  cast  from  a  natural  mould  of  essentially  the 
same  size.  The  species  is  a  very  distinct  one,  but  it  more  closely  resem- 
bles S.  chouteauensis  thau  any  other,  it  may  be  distinguished  from  that 
species,  however,  by  the  proportionately  more  elongate  shell,  the  shal- 
lower and  narrower  mesial  sinus  which  is  either  smooth  or  is  marked 
only  by  an  obscure  mesial  plication  and  never  by  lateral  ones  branching 
off  from  the  inner  margins  of  the  bounding  plications. 

Horizon. — Kinderhook. 

Brachythyris  fernglenensis  AVeller 

Plate  LIT,  Figs.  5-11 

1909.     Spirifer  fernglensis  Weller,  Bull.  Geo].  Soc.  Amer.,  vol.  20,  p.  306, 
pi.  13,  figs."  9-10. 

Description.— Shell  small,  wider  than  long,  subglobular  in  form,  hinge- 
line  a  little  shorter  than  the  greatest  width  of  the  shell,  cardinal  ex- 
tremities rounded.  The  dimensions  of  a  nearly  perfect  specimen  are: 
length  of  pedicle  valve  13.5  mm.,  length  of  brachial  valve  11  mm.,  width 
14.6  mm.,  length  of  hinge-line  13  mm.,  thickness  11  mm.,  width  of  mesial 
sinus  in  front  5.2  mm. 


BK.HIIYTI1YKIS  373 

Pedicle  valve  strongly  convex,  the  greatest  convexity  near  or  a  little 
posterior  to  the  middle,  the  umbonal  region  small,  the  surface  curving 
rather  abruptly  both  anteriorly,  laterally  and  posteriorly  from  the  point 
of  greatest  convexity ;  the  beak  small,  rather  short,  incurved ;  cardinal 
area  small  and  low,  arched,  the  lateral  margins  usually  not  discernable, 
the  surface  of  the  area  curving  without  demarkation  into  the  lateral 
slopes  of  the  valve,  occasionally  the  lateral  margins  may  be  detected  as  a 
pair  of  faint  ridges  which  slope  from  the  beak  to  the  cardinal  extremities ; 
the  delthyrium  broader  than  high,  bordered  on  each  side  by  a  distinctly 
elevated  ridge  which  passes  from  the  apex  to  the  hinge-line ;  lateral  slopes 
strongly  convex,  as  the  surface  approaches  the  lateral  and  anterior  mar- 
gins the  curvature  becomes  more  abrupt,  until  in  adult  shells  it  is  nearly 
vertical  to  the  plane  of  the  valve,  each  marked  by  about  7  broad,  de- 
pressed, rounded,  more  or  less  obscure,  simple  plications ;  mesial  sinus 
narrow,  shallow,  rounded  in  the  bottom,  smooth,  originating  at  the  beak 
and  slightly  produced  in  front  in  a  nasute  extension  nearly  at  right  angles 
to  the  plane  of  the  valve. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  the  surface  curving  more  abruptly  to  the  cardinal  mar- 
gin, sometimes  a  little  depressed  towards  the  cardinal  extremities ;  mesial 
fold  originating  at  the  beak,  smooth,  rounded,  but  little  elevated  above  the 
general  surface  posteriorly  and  only  moderately  elevated  towards  the 
front ;  lateral  slopes  marked  by  plications  similar  in  form  and  number  to 
those  of  the  opposite  valve,  but  somewhat  stronger. 

The  minute  surface  markings  are  not  clearly  preserved  on  any  of 
the  specimens  observed,  but  there  is  no  indication  of  anything  except 
concentric  markings.  More  or  less  inconspicuous  concentric  growth 
lines  are  sometimes  present. 

Remarks. — This  species  is  especially  characterized  by  its  rotund  form. 
It  differs  from  S.  choutemiensis  in  its  smaller  size,  greater  convexity 
of  the  valves,  smaller  and  less-defined  cardinal  area,  the  less  extended 
beak  of  its  pedicle  valve,  and  the  perfectly  smooth  fold  and  sinus.  The 
largest  example  observed  has  a  length  of  15  mm. 

Horizon. — Fern  Glen  formation  of  the  Kinderhook. 

Brachythyris  chouteauensis  Weller 

Plate  LVII,  Figs.  4-11 

1909.     Spirifcr  cltoiiteauensis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  305, 
pi.  13,  fig.  11. 

Description. — Shell  suborbicular  in  outline,  the  length  and  width  nearly 
equal,  hinge-line  about  two-thirds  the  greatest  width  of  the  shell,  cardinal 
extremities  rounded.  The  dimensions  of  a  nearly  complete  example  are : 
length  of  pedicle  valve  22  mm.,  length  of  brachial  valve  20  mm.,  length 


157-4  MISSISSIPPIAN   BBACHIOPODA 

of  binge-line  13.5  nun.,  greatest  width  of  shell,  24.5  nun.,  thickness  17 
nun.,  height  of  cardinal  area  2  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbo  rather  narrow,  prominent,  the  surface  curving  abruptly 
from  the  umbonal  region  to  the  cardinal  margin  and  more  gently  to  the 
anterolateral  margins,  sometimes  a  Little  compressed  towards  the  car- 
dinal extremities;  beak  small,  sharply  pointed,  rather  strongly  incurved; 
cardinal  area,  small,  arched,  the  curvature  becoming  greater  towards  the 
beak,  lateral  margins  more  or  less  ill-defined,  sloping  from  the  beak  to 
the  cardinal  extremities;  lateral  slopes  convex  anlero-posteriorly,  marked 
by  from  8  to  11  simple,  rounded  plications;  mesial  sinus  narrow,  rather 
shallow,  rounded  in  the  bottom,  well-defined  to  the  beak  posteriorly, 
becoming  less  well  defined  anteriorly,  hounded  by  a  pair  of  plications 
which  are  notably  broader  and  stronger  than  those  of  the  lateral  slopes, 
marked  by  two  or  four  obscure,  depressed,  rounded  plications  which 
originate  from  the  inner  margins  of  the  bounding  plications. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  the  surface  curving  abruptly  to  the  cardinal  margin, 
and  more  gently  to  the  antero-lateral  margins,  usually  somewhat  com- 
prised towards  the  cardinal  extremities;  mesial  fold  defined  to  the 
beak,  convex,  scarcely  elevated  above  the  general  surface  posteriorly, 
moderately  elevated  in  front,  obscurely  marked  by  plications  similar 
in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  consist  of  obscure,  exceed- 
ingly fine,  concentric  striaj  which  are  ordinarily  obliterated  in  the  fossils. 
At  irregular  intervals  several  concentric  lines  of  growth  are  usually 
present. 

Remarks. — The  plication  of  the  fold  and  sinus  of  this  species  is  very 
obscure,  and  not  infrequently  seems  to  be  absent  altogether  at  first 
sight.  In  its  general  form  and  proportions  the  species  resembles  S. 
suborbicularis,  but  it  is  always  much  smaller  than  the  adult  examples  of 
that  species.  The  cardinal  area  of  the  pedicle  valve  in  S.  ckouteauensis, 
however,  is  proportionately  smaller  and  less  well  defined  than  in  S. 
suborbicularis.  Members  of  this  species  have  not  infrequently  been  identi- 
fied as  S.  peculiaris,  but  it  differs  conspicuously  from  that  species  in  the 
lower  and  more  defined  cardinal  area,  the  more  approximate  beaks  of 
the  two  valves  and  in  the  obscure  plications  of  the  fold  and  sinus. 

Horizon. — Kinderhook. 

Brachythyris  suborbicularis  (Hall) 

Plate  LX1,  Figs.  1-8;  Plate  LX1I,  Figs.  1-12 

1858.    Spirifer  suborbicularis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2.  p.  644. 
1875.     Spirifer  suborbicularis  Meek  and  Worthen,  Geol.  Surv.  111.,  vol.  (>. 
p.  523,  pi.  30,  fig.  1. 


BRACH  VTI1VHIS  375 

Description.— Shell  above  medium  size,  suborbicular  in  outline,  a  little 
wider  than  long,  the  hinge-line  shorter  than  the  greatest  width  of  the  shell, 
the  cardinal  extremities  rounded  or  obtusely  angular.  The  dimensions 
of  a  nearly  complete,  but  small,  undistorted  specimen  are:  length  40 
inni.,  width  46  mm.,  thickness  27  mm.,  length  of  hinge-line  32  mm.  The 
dimensions  of  a  large  pedicle  valve  are:  length  approximately  56  mm., 
width  62  mm.,  convexity  23.5  mm.,  length  of  hinge-line  45  mm.,  height  of 
cardinal  area  6  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbonal  region  rather  narrow,  the  surface  usually  somewhat 
compressed  towards  the  cardinal  extremities;  beak  pointed  and  rather 
strongly  incurved;  cardinal  area  rather  low,  arched,  the  curvature  be- 
coming greater  towards  the  beak,  the  lateral  margins  denned,  sloping 
from  the  beak  to  the  cardinal  extremities  with  a  slightly  sigmoidal  curve, 
the  delthyrium  rather  large,  wider  than  high,  bordered  on  each  side 
by  a  thickened  ridge  which  is  raised  above  the  general  level  of  the  area ; 
surface  of  the  area  marked  by  longitudinal  lines  of  growth;  lateral  slopes 
of  the  valve  each  marked  with  10  to  12  depressed,  more  or  less  obscure, 
simple  plications,  those  near  the  sinus  being  broad,  the  successive  ones 
towards  the  cardinal  extremities  becoming  narrower  and  fainter,  the 
last  four  or  so  becoming  so  faint,  especially  in  large  individuals,  as  to  be 
almost  obsolete;  mesial  sinus  defined  to  the  beak,  anteriorly  it  becomes 
less  sharply  defined,  is  rather  broad,  of  moderate  depth,  and  rounded 
in  the  bottom,  at  the  anterior  margin  it  is  sometimes  produced  into  a 
nasute  extension,  it  is  marked  in  the  median  line  by  a  narrow,  ill-defined 
obscure  or  almost  obsolete  plication,  and  by  one  or  two  on  each  side 
which  are  broader  but  equally  obscure. 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity  near 
the  middle,  the  surface  compressed  towards  the  cardinal  extremities,  the 
beak  projecting  slightly  beyond  the  hinge-line ;  mesial  fold  defined  to  the 
beak,  where  it  is  narrow  and  scarcely  elevated,  becoming  broader  and 
often  rather  strongly  elevated  towards  the  front,  rounded  in  contour, 
marked  by  four  or  six  very  obscure,  sometimes,  apparently,  almost  or 
quite  obsolete  plications;  lateral  slopes  marked  by  plications  which  are 
similar  in  number  to  those  of  the  opposite  valve,  but  which  are  commonly 
much  more  strongly  developed. 

The  minute  surface  markings  of  the  shell  have  not  been  clearly  seen, 
but  the  shell  seems  to  be  smooth  except  for  the  presence  of  more  or  less 
strongly  developed  lines  of  growth. 

Internally  the  muscular  impressions  of  the  pedicle  valve  are  but, 
faintly  developed,  and  the  dental  plates  are  so  short  that  they  are  rep- 
resented in  the  internal  casts  as  but  slightly  depressed  grooves,  one  on 
each  side  of  the  delthyrium. 


:]~{)  MISSISSIPFIAN    BRACHIOPODA 

Remarks. — This  species  occurs  Bomewhal  commonly  in  the  Burlington 
and  Keokuk  Limestones,  and  has  been  identified  by  Beede  from  the  Salem 
limestone  of  Indiana.1  This  last  identification,  however,  is  incorrect 
since  the  figure  given  to  represent  the  species  shows  a  shell  with  strong 
and  elongate  dental  lamellae.  In  general  form  the  species  somewhat 
resembles  S.  subcardiiformis  and  <s'.  gurleyi;  From  Ihe  first  of  these  it  differs 
in  its  much  Longer  cardinal  area,  and  from  both  il  differs  in  having  much 
less  strongly  developed  plications  upon  the  lateral  slopes,  especially  of 
the  pedicle  valve,  and  in  the  almost  obsolete  plications  of  the  fold  and 
sinus. 

Horizon. — Burlington  and  Keokuk  limestones. 

Brachythyris  subcardiiformis   (Hall) 
Plate  LX,  Figs.  1-15 

1858.     Spirifer  subcardiiformis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  660,  pi.  23, 

figs.  6a-b. 
1880.     Spirifi  r  subcardiiformis  White,  Cont.  to  Inv.  Pal.,  No.  8,  p.  165, 

pi.  41,  figs.  2a-c. 
1906.     Spirifcr  subcardiiformis  Beede.  30th  Ann.  Rep.  Geol.  Surv.  Ind., 

p.  1313,  pi.  21,  figs.  2-2b. 

Description. — Shell  of  medium  size  or  larger,  suhorbicular  in  outline,  the 
greatest  width  near  the  mid-length  of  the  shell,  the  true  hinge-line  short, 
the  cardinal  extremities  rounded.  The  dimensions  of  two  individuals  are: 
length  43  mm.  and  28  mm.,  width  43.5  mm.  and  32  mm.,  width  of  true 
cardinal  area  along  the  hinge-line  15.5  mm.  and  10  mm.,  thickness  27.3 
mm.  and  17  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  curving  abruptly  from  the  umbonal  region  to  the  cardinal  mar- 
gin and  more  gently  to  the  anterior  and  lateral  margins,  the  convexity  of 
the  valve  extending  to  the  cardinal  extremities ;  beak  pointed  and  in- 
curved ;  cardinal  area  small,  concave,  becoming  more  curved  towards  the 
beak,  sloping  posteriorly  at  an  angle  of  about  115  degrees  to  the  plane  of  the 
valve,  its  width  along  the  hinge-line  about  one-third  the  total  width  of 
the  shell,  the  central  half  of  its  width  occupied  by  the  large  triangular 
delthyrium  so  that  the  actual  surface  of  the  area  is  limited  to  two  narrow 
bands  which  pass  obliquely  from  the  hinge-line  on  each  side  of  the 
delthyrium  to  the  beak,  the  lateral  margins  of  the  area  are  well  defined 
and  beyond  them  the  surface  of  the  valve  is  abruptly  depressed  into  a 
concave,  false  cardinal  area  broader  than  the  true  area,  which  rounds 

l  Spirifer  suborbicularis  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1312,  pi.  19 
figs.  3-3a;   pi.  21,  fig.  4.     (1906.) 


BR-UI1YTIIYKIS  377 

into  the  lateral  slopes  of  the  valve  without  any  sharp  line  of  demarca- 
tion ;  lateral  slopes  of  the  valve  each  bearing  from  8  to  10  broadly 
rounded,  simple  plications  which  grow  progressively  smaller  towards  the 
cardinal  extremities;  mesial  sinus  originating  at  the  beak  where  it  is  very 
narrow  and  well  defined,  anteriorly  it  becomes  broad  and  shallow,  fiat  or 
roundish  in  the  bottom,  and  in  large  examples  it  is  sometimes  produced 
in  a  nasute  extension  anteriorly,  it  is  usually  occupied  by  three  rounded 
plications  of  nearly  equal  size,  similar  to  the  larger  plications  upon  the 
lateral  slopes,  all  three  plications  originate  near  the  beak,  the  two  lateral 
ones  originating  from  the  inner  margins  of  the  lateral  bounding  plica- 
tions a  little  in  front  of  the  origin  of  the  median  one,  sometimes  the 
number  of  plications  is  reduced  to  two  in  number  and  sometimes  in- 
creased to  four,  but  often  when  the  number  is  abnormal  they  are  not  so 
nearly  equal  in  size  as  in  normal  individuals. 

Brachial  valve  less  convex  than  the  pedicle,  its  greatest  convexity  near 
the  middle,  the  surface  sometimes  a  little  compressed  towards  the  cardinal 
extremities,  the  beak  projecting  a  little  posteriorly  from  the  hinge-line ; 
mesial  fold  defined  to  the  beak  but  scarcely  elevated  above  the  general 
surface  of  the  valve,  becoming  gradually  elevated  to  the  front  where  it  is 
rounded  and  of  moderate  height,  in  large  individuals  it  is  sometimes 
rather  abruptly  elevated  near  the  anterior  margin,  in  normal  specimens 
it  is  marked  by  four,  subequal,  convex  plications  which  originate  from  a 
single  one  at  the  beak,  in  individuals  with  more  or  less  than  three  plica- 
tions in  the  sinus  of  the  pedicle  valve  there  is  a  like  variation  in  the  fold 
of  the  brachial  valve ;  lateral  slopes  of  the  valve  bearing  plications  similar 
in  form  and  number  to  those  of  the  opposite  valve. 

Minute  surface  markings  of  the  shell  not  observed,  but  concentric 
lines  of  growth  of  greater  or  less  strength  are  usually  present,  which 
are  sometimes  crowded  towards  the  anterior  margin  in  large  individuals. 

Remarks.— This  shell  is  a  very  characteristic  member  of  the  Salem 
fauna  in  Indiana  and  Illinois  and  has  not  been  certainly  seen  from 
any  other  horizon,  although  some  specimens  are  labeled  as  coming  from 
the  Keokuk  limestone  in  Indiana.  The  shell  is  especially  characterized 
by  its  very  narrow  cardinal  area  with  the  false  area-like  regions  on 
either  side  of  the  true  cardinal  area.  In  general  outline  the  shell  resem- 
bles S.  sub  orbicularis,  but  the  plications  are  stronger  in  8.  subcardiiformis, 
especially  those  of  the  fold  and  sinus. 

Horizon.  —  Salem  limestone, 

Bbachythtris  gurlevi  n.  sp. 
Plate  LVIII,  Figs.  4-8 
Description. — Shell  of  medium  size,  suborbicular  in  outline,  the  greatest 
width  near  the  mid-length  of  the  shell,  the  cardinal  extremities  rounded. 


378  MISSISSJPPIAN    BRACHIOPODA 

The  dimensions  of  a   nearly   complete   individual   are:    length  30  mm., 

width  32  nun..  Length  of  binge-line  -<»  mm.,  thickness  '21  nun. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  curving  abruptly  from  the  umbonal  region  to  the  cardinal 
margin,  more  gently  to  the  anterior  and  lateral  margins,  the  convexity 
extending  to  the  cardinal  extremities;  heak  pointed  and  incurved ;  car- 
dinal area  aliont  two-thirds  the  total  width  of  the  shell,  5  mm.  in  height 
in  the  type,  concave,  becoming  more  curved  towards  the  beak,  its  inferior 
portion  sloping  at  an  angle  of  ahout  lift  degrees  to  the  plane  of  the  valve, 
its  lateral  margins  defined,  ils  surface  marked  by  vertical  stria';  delthy- 
rium  rather  large,  forming  a  nearly  equilateral  triangle;  lateral  slopes  of 
the  valve  each  bearing  about  11  depressed,  rounded  plications,  most  of 
which  are  simple,  although  a  tendency  to  divide  is  occasionally  observable, 
they  become  progressively  smaller  towards  the  cardinal  extremities; 
mesial  sinus  ill-defined,  Dearly  or  quite  obsolete  at  the  beak,  shallow 
and  rounded  in  the  bottom,  occupied  by  about  7  plications  similar  in 
strength   to  those   upon   the   lateral   slopes. 

Brachial  valve  subelliptical  in  outline,  a  little  less  concave  than  the 
pedicle,  its  greatest  convexity  near  the  middle,  the  surface  slightly  com- 
pressed towards  the  cardinal  extremities,  the  beak  projecting  a  little 
posteriorly  from  the  hinge-line;  mesial  fold  scarcely  defined  at  the  beak, 
becoming  moderately  elevated  anteriorly  where  it  is  rounded  in  contour 
and  is  not  sharply  differentiated  from  the  lateral  slopes,  bearing  eight 
plications,  the  four  central  ones  being  less  distinct  than  the  others,  in 
the  umbonal  region  the  four  central  ones  have  become  united  into  a 
single  median  plication  and  each  pair  of  two  lateral  ones  are  also  united 
so  there  are  only  three  in  all,  and  it  is  possible  that  these  three  also 
unite  into  a  single  one  before  reaching  the  beak,  but  the  condition  of 
preservation  of  the  type  is  not  such  as  to  certainly  show  this;  the  lateral 
slopes  of  the  valve  bear  plications  similar  in  form  and  number  to  those 
of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  are  not  preserved  in  the 
type  specimen,  but  a  few  rather  weak"  concentric  lines  of  growth  are 
shown. 

Remarks. —  In  general  form  and  appearance  this  species  resembles  S. 
subcardiiformis  and  it  has  usually  been  so  identified.  It  is  easily  distin- 
guished from  that  species,  however,  by  its  much  broader  cardinal  area 
and  by  the  absence  of  the  false  cardinal  area  which  is  so  conspicuous  on 
that  species,  as  well  as  by  the  less  sharply  defined  mesial  sinus  with  its 
larger  number  of  plications  and  the  occasional  tendency  of  the  plications 
to  divide. 

Horizon.  —  Salem   limestone. 


BRACHYTHYRIS  :!7!> 

Brachythyris   ALTONENSIS   11.   sp. 
Plate  LIX,  Figs.  7-14 

Description. — Shell  small,  subglobular  in  form,  a  little  wider  than  long, 
the  greatest  width  near  the  mid-length  of  the  shell,  the  length  of  the 
hinge-line  equal  to  about  one-half  the  total  width  of  the  shell,  the  cardinal 
extremities  rounded.  The  dimensions  of  two  individuals  are:  length  of 
pedicle  valve  14.8  mm.  and  14.5  mm.,  length  of  brachial  valve  11  mm. 
and  10.8  mm.,  width  15.2  mm.  and  15.5  mm.,  thickness  10.5  mm.  and  9.8 
mm.,  length  of  hinge-line  8.5  mm.  and  9  mm.,  height  of  cardinal  area  '■*> 
mm.  and  2.8  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  convexity  extending  out  to  the  cardinal  extremities,  umbo 
prominent,  projecting  posteriorly  beyond  the  hinge-line,  the  surface 
sloping  abruptly  to  the  cardinal  margin,  more  gently  to  the  antero-lateral 
margins;  beak  pointed  and  incurved;  cardinal  area  small,  arched,  broadly 
triangular  in  outline,  the  lateral  margins  defined,  although  the  demarca- 
tion between  the  area  and  the  Lateral  slopes  of  the  valve  is  only  slightly 
marked,  sloping  regularly  from  the  beak  to  the  cardinal  extremities ;  the 
delthyrium  large,  its  base  occupying  more  than  one-third  the  cardinal 
margin  of  the  area;  lateral  slopes  of  the  valve  each  bearing  five  simple, 
rounded  plications  which  grow  progressively  smaller  towards  the  car- 
dinal extremities;  mesial  sinus  distinct  to  the  beak,  rather  shallow, 
flattened  in  the  bottom  anteriorly,  marked  along  the  median  line  by  a 
narrow  plication. 

Brachial  valve  much  less  convex  than  the  pedicle,  the  greatest  convexity 
near  or  a  little  in  front  of  the  middle;  mesial  fold  defined  to  the  beak, 
bounded  by  furrows  which  are  deeper  and  broader  than  those  between 
the  other  plications,  flattened  on  top  and  marked  along  the  median  line 
by  a  narrow  and  shallow  groove;  lateral  slopes  most  convex  towards  the 
umbo,  a  little  compressed  towards  the  cardinal  extremities,  marked  by 
plications  similar  in  form  and  number  to  those  of  the  opposite  valve. 

The  minute  surface  markings  of  the  shell  have  not  been  observed,  but 
concentric  lines  of  growth  of  variable  strength  are  present  which  be- 
come more  frequent  towards  the  anterior  margin. 

Internally  the  dental  lamella'  of  the  pedicle  valve  extend  one-fifth  or 
a  little  more  from  the  beak  towards  the  anterior  margin  with  slight 
divergence,  the  muscular  impressions  are  inconspicuous. 

Remarks. — The  types  of  this  species  are  two  nearly  complete  internal 
casts  from  a  dolomitie  layer  of  the  St.  Louis  limestone  near  Alton.  In 
recent  collections  the  species  occurs  a  few  feet  below  the  base  of  the 
brecciated  layer  of  the  formation,  and  the  types  doubtless  came  from  this 
same  position.     If  the  specimens  were  differently  preserved  with  the  shell 


380 


MISSISSIPPIAN    BRACHIOPODA 


substance  present,  i1  is  possible  thai  one  or  two  additional  plications 
mighl  be  presenl  towards  the  cardinal  extremities  of  each  lateral  slope 
of  the  valves.  The  state  of  preservation  is  also  responsible  for  all  absence 
of  the  minute  surface  characters  of  the  shell.  In  its  general  aspect  the 
species  is  similar  to  8.  sub orbicularis  excepl  in  its  much  smaller  size  and 
in  the  distinct  median  plication  of  the  fold. 
Horizon.-  -St.  Louis  lime-tone. 

Hracii  vtiivkis  SEMIPLICATA    (Hall) 
Plate  LIX,  Figs.  15-19 

1860.    Spirifer  semiplicata  Hall,  13th  Rep.  N.  Y.,  State  Cab.  Nat.  Hist, 

p.  111. 
18(56.    Spirifer  cooperensis,  Meek  and  Worthen,  Geol.  Snrv.  111.,  vol.  2,  p. 

155,  pi.  14,  figs.  5a-b. 

Description. — Shell  small,  wider  than  long,  the  hinge-line  a  little 
shorter  than  the  greatest  width,  the  cardinal  extremities  rounded.  The 
dimensions  of  a  nearly  complete  specimen  are:  length  of  pedicle  valve  8.5 
mm.,  length  of  brachial  valve  7  mm.,  greatest  width  9.1  mm.,  length  of 
hinge-line  6  mm.,  thickness  6.4  mm. 

Pedicle  valve  subpyramidal  in  form,  the  greatest  depth  posterior  to  the 
middle  in  the  umbonal  region,  the  surface  curving  abruptly  to  the  car- 
dinal margin  on  each  side  of  the  beak  and  more  gently  to  the  lateral  and 
anterior  margins,  not  compressed  towards  the  cardinal  extremities;  beak 
blunt  and  short,  incurved;  cardinal  area  of  moderate  size,  concave,  its 
lateral  margins  not  sharply  defined,  its  surface  curving  into  the  lateral 
slopes  of  the  valve  with  but  slight  interruption ;  mesial  sinus  originating 
as  a  flattening  of  the  valve  in  the  umbonal  region,  becoming  broad  ante- 
riorly but  remaining  very  shallow  and  flat,  marked  by  a  single  low,  rather 
faint,  median  plication,  which  originates  near  the  middle  of  the  valve; 
the  lateral  slopes  rather  sharply  differentiated  from  the  mesial  sinus,  each 
marked  by  about  four  simple,  obscure,  rounded  plications  which  become 
obsolete  a  little  past  the  middle  of  the  valve. 

Brachial  valve  depressed  convex,  much  shallower  than  the  pedicle,  its 
greatest  depth  posterior  to  the  middle,  the  surface  curving  rather  ab- 
ruptly to  the  cardinal  margin  and  more  gently  to  the  lateral  and  anterior 
margins,  a  little  compressed  towards  the  cardinal  extremities ;  the  beak 
obtuse,  only  slightly  produced  beyond  the  cardinal  margin ;  the  mesial 
fold  obscure  in  the  posterior  half  of  the  valve,  broad,  flat  and  only  slightly 
elevated  in  front,  marked  by  an  obscure  mesial  furrow ;  the  lateral  slopes 
marked  by  obscure  plications  entirely  similar  to  those  of  the  opposite 
valve. 

The  finer  surface  markings  consist  of  fine,  concentric  lines  of  growth 
upon  each  valve. 


BRACHYTHYRIS  381 

Remarks. — This  species  was  originally  described  in  a  very  inadequate 
manner  without  illustrations,  from  the  Roekford  limestone  of  Indiana, 
and  the  type  seems  to  have  been  lost.  The  little  shell  which  is  illustrated 
herewith,  and  which  has  been  used  as  a  basis  for  the  above  definition,  is 
from  a  limestone  in  Union  County,  Illinois,  which  is  believed  to  be  an  ex- 
tension of  the  Roekford  limestone  of  Indiana.  It  seems  to  agree  in  all 
essential  respects  with  Hall's  original  description  of  the  species,  and  has 
consequently  been  so  identified. 

Horizon. — Roekford  limestone  of  the  Kinderhook. 

Braciiythyris  pectliaris   (Shumard) 
Plate  LVI1,  Fig.  12  ;  Plate  LV1I1,  Figs.  9-20 ;  Plate  LXXXIII,  Figs.  3-5 

1855.     Spirifer  ?  peculiars  Shumard,  Geol.  Rep.  Mo.,  1855,  p.  202,  pi.  C, 

figs.  7a-b. 
1894.     Spin/era  peculiaris  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  79. 

Description. — Shell  subrhomboidal  in  outline,  usually  wider  than  long, 
the  greatest  width  at  about  the  mid-length  of  the  shell,  the  hinge-line 
about  one-half  as  long  as  the  greatest  width,  cardinal  extremities  rounded, 
the  beaks  of  the  two  valves  remote.  The  dimensions  of  two  perfect  indi- 
viduals, one  with  average  proportions,  the  other  much  more  elongate  than 
usual,  are :  length  of  pedicle  valve  16.5  mm.  and  18  mm.,  length  of  brachial 
valve  15  mm.  and  16.5  mm.,  greatest  width  19  mm.  and  16  mm.,  length  of 
hinge-line  9.5  mm.  and  8  mm.,  thickness  14  mm.  and  15  mm.,  height  of 
cardinal  area  4  mm.  and  3.2  mm. 

Pedicle  valve  strongly  convex,  the  umbo  prominent,  the  surface  curving 
very  abruptly  to  the  cardinal  margin  and  more  gently  to  the  antero- 
lateral margins;  the  beak  acuminately  pointed,  rather  small,  strongly  in- 
curved ;  cardinal  area  rather  high  and  narrow,  the  inferior  portion  direct- 
ed in  nearly  a  right  angle  to  the  plane  of  the  valve,  the  upper  portion 
strongly  arched,  the  lateral  margins  sloping  steeply  from  the  beak  to  the 
extremities  of  the  hinge-line,  scarcely  defined  from  the  inflected  parts 
of  the  lateral  slopes  which  form  a  false  cardinal  area ;  each  lateral  slope 
divided  into  two  regions  by  a  rounded  ridge  which  passes  from  the  beak 
to  the  point  of  greatest  lateral  extension  of  the  valve,  on  the  posterior 
side  of  this  ridge  the  surface  is  abruptly  inflected  and  forms  one  side  of 
a  false  cardinal  area  which  is  scarcely  differentiated  from  the  true  car- 
dinal area,  the  anterior  slope  on  each  side  is  marked  by  from  5  to  8  simple, 
depressed,  rounded  plications  which  terminate  posteriorly  along  the 
rounded  ridge  between  the  anterior  and  posterior  portions  of  the  lateral 
slope;  mesial  sinus  narrow,  shallow,  rounded  in  the  bottom,  continuing  to 
the  beak,  without  plications. 

Brachial  valve  much  less  convex  than  the  pedicle,  the  umbo  prominent, 
the  beak  projecting  conspicuously  beyond  the  hinge-line  posteriorly ;  the 


382  .Mississippi A.\    BRACHIOPODA 

mesial  fold  low.  rounded,  defined  to  the  beak,  smooth  or  sometimes  faintly 
marked  by  a  median  furrow;  lateral  slopes  convex,  each  divided  into  a 
posterior  and  an  anterior  portion  by  a  rounded  ridge  passing  from  the 
beak  to  the  point  of  greatesl  lateral  extension  of  the  shell,  bul  the  differ- 
entiation is  not  so  strongly  marked  as  in  the  pedicle  valve,  the  posterior 
portion  curves  abruptly  to  the  cardinal  margin  and  is  free  from  plica- 
tions, the  anterior  portion  curves  more  gently  to  the  anterodatcral  margin 
and  is  marked  by  plications  similar  in  form  and  number  to  those  of  the 
opposite  valve. 

The  minute  surface  markings  of  the  shell  consist  of  very  tine  concentric 
lines.  Both  valves  also  bear,  at  intervals,  stronger  concentric  lines  of 
growth  which  traverse  both  the  anterior  and  posterior  portions  of  the 
lateral  slopes,  and  which  terminate  posteriorly  in  the  pedicle  valve  at  the 
lateral  margins  of  the  true  cardinal  area. 

I! <  murks. — This  shell  is  one  of  the  most  sharply  defined  species  in  all 
our  Mississippian  faunas  and  cannot  be  confused  with  any  other.  Ex- 
amples of  the  shell  here  described  as  8.  choutt  inn  iisis  have  sometimes  been 
identified  as  .s'.  peculiaris,  but  that  species  has  much  more  approximate 
beaks  with  a  Longer  binge-line  and  lower  cardinal  area,  and  does  not  pos- 
sess 1  he  conspicuous  false  cardinal  area  of  8.  peculiaris.  The  fold  and 
sinus  in  the  two  species  are  also  different  in  character.  These  same  char- 
acters distinguish  8.  peculiaris  from  8.  bwrli/ngtonensis,  and  in  addition 
the  more  anterior  position  of  the  greatest  width  of  the  shell  in  8.  peculiaris, 

Horizon.  -Chouteau  Limestone  of  the  Kinderhook. 

Genus  CTRTIA  Dalman 

Description. — Shell  small  or  of  medium  size,  semipyramidal  in  form,  the 
greatesl  width  along  the  hinge-line,  the  sinus  of  the  pedicle  valve  and 
the  fold  of  the  brachial  valve  well  developed  and  non-plicate,  the  lateral 
slopes  of  the  valves  plicated  or  not.  The  pedicle  valve  with  a  very  high 
cardinal  area  which  may  be  flat  or  arched,  the  delthyrium  narrowly  tri- 
angular and  covered  by  a  transversely  convex  pseudodeltidium  ;  inter- 
nally the  dental  lamellae  are  conspicuously  developed  and  may  reach  ante- 
riorly beyond  the  middle  of  the  valve ;  no  median  septum  present. 
Brachial  valve  as  in  Spirifer.     Shell  structure  non-punctate. 

Remarks.  —  The  genus  Cyrtia  was  originally  e-.tablished  upon  the  species 
('.  exporrecta  from  the  Silurian  of  Sweden,  and  one  or  more  species  in  the 
Silurian  faunas  of  America  are  clearly  congeneric  with  the  genotype 
from  Sweden.  The  characters  which  serve  to  differentiate  the  genus  from 
Spirifer  are  its  very  high  cardinal  area,  the  strongly  developed  dental 
lamellae  and  the  pseudodeltidial  covering  of  the  delthyrium.  In  general 
form  the  members  of  the  genus  resemble  Cyrtina  more  closely  than  Spirifer, 
but  they  lack  the  spondylium  and  median  septum  of  that  genus,  as  well 
as  the  punctate  shell  structure. 


CYRTIA 


383 


The  species  which  is  here  recognized  is  based  upon  a  single  specimen  of 
an  incomplete  pedicle  valve  which  differs  from  the  genotype  in  the  greater 
development  of  the  dental  lamella?,  in  the  plicated  lateral  slopes  of  the 
\alve  and  in  the  absence  of  the  foramen  through  the  pseudodeltidium. 
The  specimen  resembles  the  members  of  the  genus  Pseudosyrinx  but 
lacks  the  delthyrial  plate  and  the  punctate  shell  structure,  and  possesses 
a  convex  pseudodeltidial  covering  of  the  delthyrium.  It  seems  to  agree 
with  Cyrtia  more  closely  than  with  any  other  genus,  hence  its  reference 
lo  that  genus  in  this  place. 

Cyrtia  inexpectans  n.  sp. 
Plate  LXIII,  Figs.  1-4 

Description. — Shell  of  medium  size,  the  hinge-line  a  little  shorter  than 
the  greatest  width  of  the  shell,  the  cardinal  extremities  rounded.  The 
species  is  known  only  from  a  single  incomplete  pedicle  valve  whose  di- 
mensions, so  far  as  they  can  be  determined,  are:  width  along  hinge-line 
32  mm.,  height  of  cardinal  area  14  mm.,  length  of  pedicle  valve  from  beak 
to  front  margin  -(-21  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the  umbo 
to  the  lateral  extremities  in  nearly  straight  lines  which  meet  at  the  umbo 
in  an  angle  of  about  110  decrees,  to  the  anterior  margin  the  surface  is 
gently  convex;  mesial  sinus  non-plicate,  shallow,  scarcely  more  than  a 
median  flattening  of  the  valve;  the  beak  pointed,  curved  so  as  to  be  di- 
rected at  nearly  a  right  angle  to  the  cardinal  area;  cardinal  area  high, 
nearly  fiat  below,  becoming  gently  concave  towards  the  apex  beneath  the 
beak,  the  lateral  margins  not  sharply  defined,  the  surface  rounding  into 
that  of  the  lateral  slopes;  delthyrium  narrowly  triangular,  at  least  twice 
as  high  as  its  widtli  at  the  base,  entirely  covered  by  a  convex  pseudo- 
deltidium through  which  there  is  no  foramen;  each  lateral  slope  marked 
by  12  or  14  simple,  depressed,  radiating  plications  which  originate  along 
the  cardinal  margin  and  become  very  faint  towards  the  cardinal  extremi- 
ties. Internally  the  dental  lamelhe  are  strongly  developed,  extending 
anteriorly  from  the  beak  to  the  anterior  margin  of  the  shell  so  far  as  it  is 
preserved,  they  diverge  from  the  beak  at  an  angle  of  about  26  degrees, 
uearly  following  the  lateral  margins  of  the  mesial  sinus;  the  muscular 
scars  are  only  Faintly  marked  and  are  not  divided  longitudinally  by  a 
median  ridge  or  septum. 

The  surface  markings  of  the  shell,  aside  from  the  plications,  so  far  as 
shown  in  the  single  specimen,  consist  of  a  few  concentric  lines  of  growth; 
so  far  as  can  be  seen  the  shell  structure  is  impunctate. 

Remarks. — The  specimen  upon  which  this  species  is  based  is  unique.  It 
resembles  some  of  the  shells  which  have  been  described  under  the  new 
genus  Pseudosyrinx,  especially  /'.  missouriensis,  but    it    differs    from    that 


384  MISSISSEPPIAN   BRACHIOPODA 

shell  in  the  exceedingly  elongate  dental  lamella',  the  very  shallow  mesial 
sinus  and  in  the  solid  covering  of  the  delthyrium  by  a  pseudo-deltidium. 

The  type  specimen  is  an  internal  easi  in  chert,  with  the  external  mould, 
so  thai  both  the  internal  and  external  characters  can  be  clearly  seen. 
The  internal  east  shows  an  entire  absence  of  any  dellhyrial  plate  such  as 
i.s  present  in  I'si  itrfosyrmx  and  Syringothyris,  joining  the  dental  lamellae 
transversely.  The  pseudo-deltidium  is  strong  and  rigid,  and  has  not 
been  destroyed  in  the  leasl  by  fossilization ;  in  the  genus  Spirifcr  this  plate 
is  exceedingly  delicate  and  is  rarely  or  never  preserved,  in  Syringothyris  and 
Pst  udosyrinx  it  is  more  commonly  present,  but  is  always  a  thin,  delicate 
plate  which  is  much  crumpled  and  crushed  in  fossilization  when  it  is 
preserved  at  all,  hut  in  this  species  it  was  apparently  as  rigid  and  firm 
as  any  part  of  the  shell.  The  absence  of  a  foramen  through  the  pseudo- 
deltidium  is  not  an  uncommon  feature  in  Cyrtia.  The  absence  of  a  punc- 
tate shell  structure  cannot  be  safely  affirmed  Tor  the  species  from  the 
observation  of  a  single  specimen,  but  in  this  example  there  is  not  the  slight- 
est indication  of  it.  The  combination  of  characters  present  in  the  speci- 
men seems  to  indicate  only  the  genus  Cyrtia,  to  which  genus  the  specimen 
is  referred. 

Horizon. —  Residual  chert,  probably  of  Keokuk  age. 

Genus  SYRINGOTHYRIS  Winehell 

Description. — Shells  varying  in  size  from  small  to  very  large,  spiriferoid 
in  form,  with  a  much  elevated  cardinal  area,  the  hinge-line  straight  and 
elongate,  representing  the  greatest  width  of  the  shell,  the  fold  and  sinus 
well  developed  and  usually  non-plicate.  The  pedicle  valve  subsemi- 
pyramidal  in  form,  the  high  cardinal  area  either  flat,  concave  or  convex, 
differentiated  into  three  regions,  a  central  including  the  delthyrium,  and 
two  lateral,  by  a  pair  of  lines  originating  at  the  apex  and  passing 
obliquely  to  the  cardinal  margin,  which  they  intersect  at  equal  distances 
from  the  basal  angles  of  the  delthyrium ;  the  central  region  is  distinctly 
marked  by  vertical  stria?,  while  the  lateral  regions  are  marked  only  by 
the  horizontal  lines  of  growth;  internally  the  dental  lamella^  are  mod- 
erately well  developed,  they  rest  upon  the  floor  of  the  valve  and  are  a 
little  produced  anteriorly  along  the  lateral  margins  of  the  muscular 
scar;  they  are  united  transversely  by  a  delthyrial  plate  whose  position  is 
subparallel  with  the  cardinal  area  but  somewhat  depressed  below  it ; 
this  plate  extends  to  various  distances  from  the  apex  of  the  delthyrium 
towards  the  hinge-line  and  at  the  middle  point  of  its  cardinal  margin  it  is 
produced  still  further  towards  the  cardinal  margin  of  the  valve  as  a  free 
spine-like  process;  on  the  inner  side  of  the  spine-like  extension  of  the 
delthyrial  plate,  and  continuing  along  the  median  line  of  the  inner 
surface  of  the  plate  towards  the  apex  of  the  valve,  is  a  tube  which  is 


SYRINGOTHYRIS  385 

split  longitudinally  internally,  this  split  tube,  together  with  the  extension 
of  the  delthyrial  plate,  being  termed  the  syrinx.  In  some  cases  the 
syrinx  is  solid.  A  pseudodeltidial  covering  of  the  delthyrium  entirely 
separate  from  the  delthyrial  plate  and  syrinx  is  sometimes  present.  The 
muscular  scars  as  in  Spirifer.  The  brachial  valve  essentially  as  in 
Spirifer,  both  externally  and  internally.  Shell  structure  punctate 
throughout  except  in  the  central,  vertically  striated  region  of  the  car- 
dinal area.  The  external  surface  covered  with  a  minute,  textile-like 
ornamentation  except  upon  the  central  region  of  the  cardinal  area. 

Remarks.— The  genus  Syringothyris  represents  a  specialization  of  the 
Spirifer  type  which  is  characterized  by  the  development  of  the  syrinx,  the 
punctate  shell  structure,  the  high  cardinal  area  and  the  peculiar  character 
of  the  minute  surface  ornamentation.  Except  the  shell  structure  and 
the  minute  ornamentation  of  the  shell,  which  frequently  can  not  be 
recognized  because  of  the  condition  of  preservation,  the  distinguishing 
characters  are  confined  to  the  pedicle  valve,  indeed,  from  the  brachial 
valves  alone  not  even  the  species  can  be  successfully  identified.  The 
brachial  valves  differ  from  any  of  the  corresponding  valves  of  the  Mississ- 
ippian  Spirifers,  however,  with  which  they  might  be  confused,  by  reason 
of  the  absence  of  plications  upon  the  fold  and  sinus. 

Much  has  been  written  of  the  genus  and  its  characters,  have  come  to 
be  firmly  established.  Much  confusion  still  exists,  however,  among  the 
species  composing  the  genus,  and  in  almost  no  case  have  the  essential 
specific  characters  even  been  accurately  pointed  out.  Schuchert1  re- 
ferred most  of  the  Mississippi  basin  forms  to  these  three  species,  S. 
carteri,  S.  extenuates,  and  S.  textus,  considering  no  less  than  five  other 
forms  as  synonyms  under  these  three,  but  a  careful  investigation  of  a 
large  amount  of  excellent  material  in  which  nearly  every  described  form 
is  well  represented,  besides  some  undescribed  ones,  has  led  the  writer  to 
the  conclusion  that  most,  if  not  all,  the  named  species  are  good,  although 
their  really  essential  characters  have  not  been  clearly  pointed  out.  In 
characterizing  the  species  of  the  genus  the  brachial  valves  are  of  almost 
no  value  whatever,  and  when  that  valve  alone  is  preserved  for  study, 
it  is  in  most  cases  impossible  to  identify  it.  The  essential  specific  char- 
acters are  found  in  the  pedicle  valve  and  consist  in  the  proportional  height 
of  the  cardinal  area,  its  degree  of  curvature,  whether  flat,  concave,  or  con- 
vex, and  especially  in  the  size  of  the  angle  between  the  flatter  portion  of 
the  area  and  the  plane  of  the  valve,  this  angle  varying  among  different 
species  from  25  to  110  degrees  or  more,  but  being  fairly  constant  among 
different  individuals  of  the  same  species.  Another  set  of  characters  which 
seem  to  be  of  prime  importance  in  specific  differentiation  are  the  char- 

1  9th  Ann.  Rep.  N.  Y.  State  Geol.,  pp.  28-37.      (1890.) 

—13 


386  MINSIKSII'l'IAN    HKACIIIOPODA 

actera  of  the  delthyrial  plate  and  the  syrinx.  In  all  those  species  where 
a  sufficienl  Dumber  of  individuals  have  been  observed  showing  these 
characters,  they  seem  to  be  constant  within  reasonably  narrow  limits  of 
variation,  and  they  have  been  assumed  to  be  of  good  specific  value  In 
other  forms  in  which  they  have  been  observed  sometimes  in  bnt  a  single 
individual;  the  differenl  characteristics  of  this  plate  are  shown  in  its 
transverse  contour  externally,  whether  Hat,  concave  or  longitudinally 
keeled,  and   in  the  length  and  width  of  the  free  extension  of  the  syrinx. 

The  earliest  described  species  of  the  genus  were  S.  tcxtus  and  S.  carteri, 
both  described  by  Hall  as  members  of  the  genus  Spirifcr  beforfc  the  genus 
Syringotkyris  was  established  by  Winched.  S.  tcxtus  is  a  well-defined 
species,  but  S.  carteri  has  always  remained  as  more  or  less  of  an  enigma, 
and  several  of  our  Mississippi  basin  forms  have  been  identified  with  it  on 
insufficient  grounds;  the  true  characters  of  the  species  still  remain  un- 
certain and  in  the  present   report  it  has  not  been  recognized. 

One  reason  for  uncertainty  in  the  identification  of  the  various  species 
(if  Syringotkyris  is  that  two  distinct  generic  types  have  commonly  been 
confused,  the  two  types  of  shells  being  essentially  alike  in  all  respects 
except  that  one  has  a  delthyrial  plate  with  a  Avell-developed  syrinx  upon 
its  inner  surface,  while  the  other  has  the  delthyrial  plate  with  no  in- 
dication of  a  syrinx.  This  latter  group  of  shells  has  been  defined  as  a 
new  genus  in  this  report  and  will  be  discussed  later. 

Syringotkyris  extenuatus  (Hall) 
Plate  LXXII,  Pigs.  5-12 

1858.     Spirifcr  extenuatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  520,  pi.  7, 

fig.  6. 
1890.     Syringotkyris  extenuata  Schuchert,  9th  Ann.  Rep.  N.  Y.  State  Geol. 

for  1899,  p.  33  (in  part). 
1900.     Syringothyris  extenuatus  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  77,  pi  1,  figs.  1-3. 

Description. — Shell  of  medium  size,  much  wider  than  long,  the  greatest 
width  along  the  hinge-line,  the  cardinal  extremities  acutely  angular.  The 
dimensions  of  a  nearly  perfect  pedicle  valve  are :  length  from  beak 
to  front  margin  14  mm.,  height  of  cardinal  area  19.4  mm.,  width  along 
hinge-line  47  mm.,  width  of  sinus  in  front  10  mm.  The  dimensions  of  a 
nearly  complete  internal  cast  are :  length  of  pedicle  valve  from  beak  to 
front  margin  14  mm.,  length  of  brachial  valve  13.2  mm.,  height  of  cardinal 
area  14.2  mm.,  width  along  hinge-line  40  mm.,  thickness  16.2  mm.,  width 
of  sinus  in  front  10  mm. 

Pedicle  valve  broadly  subpyramidal  in  form,  the  surface  sloping  from 
the  beak  to  the  cardinal  extremities  in  nearly  straight  lines,  or  with  a 
slight  convex  or  concave  curvature,  the  lateral  slopes  very  short  from 


SYRINGOTHYRIS  387 

front  to  beak,  nearly  straight  or  slightly  convex  from  the  cardinal  to  the 
front  margins  towards  the  central  portion  of  the  valve,  becoming  a  little 
concave  towards  the  cardinal  extremities  because  of  the  slight  vertical 
compression  of  the  valve  along  the  cardinal  margin,  the  anterior  slope 
along  the  median  line  nearly  straight  or  slightly  curved;  mesial  sinus 
narrow  and  rather  sharply  defined  at  the  beak,  becoming  rapidly  broader 
towards  the  front  and  much  less  well-defined,  non-plicate,  concave  in  the 
bottom  and  produced  anteriorly  in  a  broad,  rounded,  linguiform  extension 
of  moderate  length;  beak  pointed,  erect,  rarely  with  a  slight  incurvature; 
cardinal  area  high,  sloping  posteriorly  from  the  hinge-line  at  an  angle 
of  from  25  to  30  degrees  to  the  plane  of  the  valve,  broadly  triangular, 
the  lateral  margins  sharply  defined,  the  surface  flat  or  very  slightly 
convex,  rarely  with  a  very  slight  concavity  just  beneath  the  beak; 
delthyriuni  narrowly  triangular,  on  each  side  of  the  delthyrium  is  a 
differentiated  region  bounded  by  lines  which  originate  at  the  beak  and 
diverge  towards  the  hinge-line  at  a  greater  angle  than  the  divergence  of 
the  margins  of  the  delthyrium,  the  base  of  this  broader  triangle  being 
nearly  twice  the  width  of  the  delthyrium  at  its  base,  the  surface  of  this 
differentiated  region  is  vertically  marked  while  the  remaining  portion  of 
the  area  is  marked  by  transverse  lines  of  growth ;  each  lateral  slope 
bearing  about  eighteen  simple,  depressed,  radiating  plications,  which 
originate  along  the  cardinal  margin  and  become  gradually  finer  and  more 
obscure  towards  the  cardinal  extremities.  Internally  the  dental  plates 
are  rather  thick  and  widely  diverging,  and  extend  nearly  or  quite  half 
way  from  the  beak  to  the  anterior  margin  of  the  valve  on  either  side  of 
the  mesial  sinus;  the  transverse,  syrinx-bearing  plate  between  the  dental 
lamellae  extends  between  one-half  and  one-third  the  distance  from  the 
beak  to  the  hinge-line,  it  is  usually  transversely  concave  externally  or 
rarely  with  a  slight  median  ridge  towards  its  lower  extremity,  the  free 
extension  of  the  syrinx  towards  the  hinge-line  is  very  short,  being  no 
more  than  a  median  angular  point  from  the  margin  of  the  transverse 
plate,  the  internal  casts  exhibit  the  characteristic  split  tube  upon  the 
inner  surface  of  the  transverse  plate ;  muscular  scars  rather  large, 
subovate  in  outline,  not  sharply  defined  on  any  of  the  specimens  observed. 
Brachial  valve  broadly  subtriangular  in  outline,  with  the  apex  of  the 
triangle  in  front  truncated  and  emarginate,  the  surface  convex  through- 
out from  the  cardinal  to  the  anterior  margins,  the  curvature  more  abrupt 
to  the  cardinal  margin,  the  greatest  convexity  at  or  near  the  anterior 
margin  at  the  median  line  of  the  valve,  the  surface  sloping  from  the 
median  line  to  the  cardinal  extremities  in  a  gently  convex  curve;  mesial 
fold  non-plicate,  well-defined,  narrow  posteriorly  and  becoming  rapidly 
broader  towards  the  front;  the  beak  short,  scarcely  extended  beyond  the 
hinge-line;   cardinal   area  linear;   each  lateral  slope   marked   by  simple 


388  MISSISSIPPI  AN   BBACHIOPODA 

plications  similar  in  tium hci"  to  those  of  the  opposite  valve  but  somewhat 
Stronger.  Internally  the  cardinal  process  is  broad  and  concave  towards 
the  front,  on  the  floor  of  the  valve  a  slight  median  ridge  extends  anter- 
iorly from  the  cardinal  process  for  about  one-third  the  length  of  the 
valve;  the  muscular  scars  not  well  defined. 

The  minute  surface  markings  are  not  shown  upon  the  exfoliated  speci- 
mens available  for  study,  but  the  shell  substance  is  minutely  and  closely 
punctate,  the  puiicta-  are  well  developed  not  only  upon  the  body  of  the 
shell  but  also  upon  the  cardinal  area  except  in  the  vertically  marked, 
differentiated  region  lying  on  either  side  of  the  delthyrium. 

Remarks.- — This  species  was  originally  described  from  a  brachial  valve 
only,  but  more  recent  collections  from  the  (honopectus  sandstone  and  the 
superjacent  bed  at  Burlington,  Iowa,  have  afforded  an  abundance  of 
materia]  which  shows  all  of  the  essential  characters  of  the  species.  It  is 
a  well-marked  species  characterized  by  its  acutely  angular  cardinal  ex- 
tremities,  the  shortness  of  the  pedicle  valve  from  the  beak  to  the  anterior 
margin,  this  distance  being  shorter  than  or  at  least  no  longer  than  the 
height  of  the  cardinal  area,  and  by  the  small  angle  between  the  cardinal 
area  and  the  plane  of  the  valve.  The  species  is  not  a  large  one,  although 
it  sometimes  attains  a  somewhat  greater  size  than  the  dimensions  given, 
the  largest  specimen  observed,  a  brachial  valve,  having  a  width  of  64  mm. 
along  the  hinge-line.  Occasional  examples  are  slightly  distorted  or 
twisted  towards  the  beak  of  the  pedicle  valve. 

Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 

Syringotiiyris  hannibalensis  (Swallow) 
Plate  LXVIII,  Figs.  1-7 

1860.     Spirifer  (Cyrtia?)  Hannibalensis  Swallow,  Trans.  St.  Louis  Acad. 

Sci.,  vol.  1,  p.  647. 
1890.     Syringotiiyris  Carteri  Schuchert,  9th  Ann.  Rep.  N.  Y    State  Geol., 

p.  30  (in  part). 
1895.     Syringothyris  Hannibalensis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8, 

pt.  2,  pi.  25,  figs.  33-35. 
1908.     Syringothyris  hannibalensis  Rowley,  Mo.  Bureau  Geol.  and  Mines, 

vol.  8,  2nd  ser.,  p.  82,  pi.  18,  figs.  6-9 ;  p.  88,  pi.  19,  figs.  4-5. 

Description. — Shell  rather  large,  much  wider  than  long,  the  greatest 
width  near  the  hinge-line,  the  cardinal  extremities  narrowly  rounded. 
The  dimensions  of  a  nearly  complete,  exfoliated  specimen  are :  length  of 
pedicle  valve  from  beak  to  front  30.5  mm.,  length  of  brachial  valve 
25.4  mm.,  width  51.5  mm.,  length  of  hinge-line  48  mm.,  height  of  cardinal 
area  16.3  mm.,  thickness  28  mm.,  width  of  sinus  in  front  17  mm.,  width 
of  delthyrium  at  base  11.6  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the 
umbonal  region  to  the  cardinal  extremities  in  nearly  straight  lines  which 


SYRINGOTHYRIS  389 

diverge  at  an  angle  of  about  110  degrees,  to  the  antero-lateral  and 
anterior  margins  the  surface  slopes  with  a  gently  convex  curvature ; 
mesial  sinus  originating  at  the  beak  where  it  is  sharply  defined,  rounded 
in  the  bottom  and  becoming  broader  and  less  sharply  denned  anteriorly, 
produced  in  front  in  a  rounded  lingual  extension  of  moderate  length; 
beak  pointed,  nearly  erect  or  slightly  incurved;  cardinal  area  large,  gently 
concave,  the  curvature  becoming  a  little  stronger  towards  the  beak, 
sloping  posteriorly  from  the  hinge-line  at  an  angle  of  from  60  to  65 
degrees,  the  lateral  margins  rounding  rather  abruptly  into  the  lateral 
slopes  of  the  valve;  delthyrium  triangular,  higher  than  wide,  on  each 
side  of  it  is  a  vertically  marked,  differentiated  portion  of  the  cardinal 
area,  bounded  by  lines  diverging  from  each  side  of  the  beak  at  an  angle 
greater  than  the  divergence  of  the  sides  of  the  delthyrium,  the  base  of  the 
entire  triangular  area  so  formed  being  more  than  double  the  base  of  the 
delthyrium  alone ;  each  lateral  slope  bearing  20  or  more  simple,  depressed, 
radiating,  more  or  less  obscure  plications  which  originate  along  the  car- 
dinal margins  and  grow  successively  smaller  towards  the  cardinal  ex- 
tremities. Internally  the  hinge-teeth  are  supported  by  rather  strong 
dental  plates  which  extend  along  the  floor  of  the  valve  between  one-thii'd 
and  one-half  its  length  from  the  beak  along  the  sides  of  the  sinus,  the 
divergence  of  the  dental  plates  closely  following  the  divergence  of  the 
margins  of  the  sinus ;  the  transverse,  syrinx-bearing  plate  between  the 
dental  lamellae  bears  a  median  longitudinal  ridge  externally  and  reaches 
about  half  way  from  the  beak  to  the  hinge-line,  the  free  inward  projecting 
point  of  the  syrinx  being  rather  broad,  short  and  blunt ;  muscular  scars  of 
moderate  size,  with  a  distinct,  median,  longitudinal  ridge. 

Brachial  valve  subsemicircular  in  outline,  emarginate  at  the  middle 
anteriorly,  the  greatest  convexity  on  the  median  line  at  or  near  the  front, 
the  surface  curving  more  abruptly  to  the  cardinal  margin,  depressed 
towards  the  cardinal  extremities;  mesial  fold  narrow  and  sharply  defined 
posteriorly,  becoming  broader  and  less  well-defined  anteriorly,  gradually 
elevated  from  nothing  at  the  beak,  rounded  or  somewhat  flattened  on 
top ;  the  beak  short,  scarcely  projecting  beyond  the  cardinal  margin, 
incurved;  cardinal  area  narrow,  lying  in  nearly  the  plane  of  the  valve; 
each  lateral  slope  marked  by  simple,  rounded,  plications,  alternate  with 
those  of  the  opposite  valve  but  much  more  strongly  developed.  Internally 
the  cardinal  process  is  broad  and  flat,  marked  with  fine  vertical  ribs  and 
grooves,  the  crural  plates  are  strong  and  diverge  from  either  side  of  the 
caidinal  process  with  the  dental  sockets  excavated  from  their  outer 
surfaces ;  the  muscular  scars  are  not  strongly  defined,  divided  longi- 
tudinally by  a  low,  median  ridge,  which  extends  from  the  beak  for  two- 
thirds  the  length  of  the  valve. 


390  MISSISSII'I'IAN    BKACHIOPODA 

The  minute  surface  markings  of  the  shell  consist  of  concentric  series 
of  exceedingly  fine  and  narrow,  suhrhomboidal  depressions  which  are 
deeper  at  their  proximal  or  posterior  extremities,  these  depressions  being 
arranged  alternately  in  succeeding  rows.  Rather  strong  concentric  lines 
of  growth  are  present  upon  all  non-exfoliated  specimens,  which  are  of 
varying  degrees  of  strength  and  are  irregularly  distributed  from  the 
beak  to  the  front.    Shell  structure  punctate. 

"Remarks.  This  is  one  of  the  Tonus  which  Schuchert  has  made  synony- 
mous with  8.  carteri,  but  it  is  undoubtedly  a  well  characterized  species,  and 
SO  far  as  known  is  confined  to  the  fauna  of  the  Louisiana  limestone. 

Horizon. — Louisiana  limestone  of  the  Kinderhook. 

Syringothyris  halli  Winchell 
Plate  LXXII,  Figs.  13-23 

1863.     Syringothyris  Halli  Winchell,  Prop.  Acad.  Nat.  Sci.  Phil.,  p.  8. 
1901.     Syringothyris  halli   Weller,   Trans.   St.  Louis  Acad.   Sci.,  vol.  11, 
p.  158,  pi.  13,  figs.  1-3. 

Description. — Shell  below  medium  size,  much  broader  than  long,  the 
greatest  width  along  the  hinge-line,  the  cardinal  extremities  acutely 
angular.  The  dimensions  of  a  nearly  complete  example  are :  length  of 
pedicle  valve  from  beak  to  front  margin  12.8  mm.,  length  of  brachial 
valve  12.2  mm.,  height  of  cardinal  area  10.9  mm.,  width  along  hinge-line 
30.6  mm.,  thickness  13  mm.,  width  of  sinus  in  front  7.2  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the 
beak  to  the  cardinal  extremities  and  to  the  anterior  margin  in  nearly 
straight  lines  or  with  but  slight  curvature ;  the  mesial  sinus  of  mod- 
erate depth,  rounded  in  the  bottom,  rather  sharply  defined  through- 
out, originating  at  the  beak  and  increasing  in  width  regularly  to 
the  front,  produced  anteriorly  in  a  rather  short,  rounded,  lingual  exten- 
sion ;  beak  pointed,  erect,  or  very  slightly  incurved;  cardinal  area  high, 
sloping  posteriorly  from  the  hinge-line  at  an  angle  of  from  50  to  60  de- 
grees to  the  plane  of  the  valve,  broadly  triangular  in  outline,  flat  or 
slightly  concave,  the  lateral  margins  sharply  defined ;  delthyrium  nar- 
rowly triangular,  the  height  about  one  and  one-half  the  width  ;  each  lateral 
slope  bearing  about  16  simple,  depressed  plications  which  originate  along 
the  cardinal  margin  and  grow  successively  finer  towards  the  cardinal 
extremities.  Internally  the  dental  lamella?  are  well  developed,  diverging 
from  the  beak  at  a  wider  angle  than  the  sides  of  the  mesial  sinus,  and 
extending  nearly  one-half  the  length  of  the  shell  from  the  beak  to  the 
front  margin  on  each  side  of  the  sinus ;  the  transverse  plate  between  the 
dental  lamella?  reaches  less  than  half  way  from  the  beak  to  the  hinge-line, 
its  external  surface  is  marked  by  a  distinct,  longitudinal,  median  ridge 


SYRINGOTHYBIS  391 

which  is  produced  below  in  the  free  tube  of  the  syrinx  whose  length  is  not 
determined;  muscular  scars  not  well  defined  on  the  specimens  studied. 

Brachial  valve  shallower  than  the  pedicle,  its  greatest  depth  near  the 
front  margin  at  the  median  line,  the  surface  curving  more  abruptly  to  the 
cardinal  margin,  somewhat  compressed  towards  the  cardinal  extremities ; 
mesial  fold  distinctly  elevated  to  the  beak,  well  defined,  of  moderate 
height,  rounded  on  top;  the  beak  very  short  and  but  slightly  projecting 
beyond  the  cardinal  margin;  cardinal  area  linear;  each  lateral  slope 
marked  by  simple  plications  similar  to  those  of  the  opposite  valve  but 
somewhat  stronger. 

The  minute  surface  markings  of  the  shell  are  not  well  shown  upon 
any  of  the  specimens  studied,  but  concentric  lines  of  growth  of  variable 
strength  are  usually  present  towards  the  front  margin.  Shell  substance 
punctate. 

Remarks.— This  species  was  considered  as  a  synonym  of  S.  extenuatus 
by  Schuehert  in  his  discussion  of  the  genus  SyringotJiyris,1  and  "Winchell 
evidently  included  specimens  which  must  be  identified  as  S.  extenuatus 
in  his  8.  halli.  The  type  specimens  of  the  species,  however,  in  the  Univer- 
sity of  Michigan  collection,  are  from  bed  No.  4,  of  the  Kinderhook,  at 
Burlington,  Iowa,  and  all  of  the  specimens  which  have  been  observed  by 
the  writer  are  from  the  same  formation  and  locality.  Specimens  of 
S.  extenuatus  in  the  University  of  Michigan  collection  were  labeled  by 
Winchell  as  S'.  halli  var.,  .showing  that  he  recognized  a  difference  between 
them.  The  two  species  are  entirely  distinct,  with  no  intermediate  variations, 
and  can  be  easily  distinguished.  S.  halli  is  a  smaller  shell,  less  extended 
along  the  hinge-line,  proportionally  longer  from  the  beak  of  the  pedicle 
valve  to  the  front  margin  as  compared  with  the  height  of  the  cardinal 
area,  with  a  much  more  sharply  defined  mesial  sinus  towards  the  front 
of  the  pedicle  valve,  with  the  transverse  syrinx-bearing  plate  between 
the  dental  lamelke,  with  a  distinct  median  longitudinal  ridge,  and  with 
the  angle  between  the  cardinal  area  and  the  plane  of  the  valve  much 
greater.  The  general  proportions  of  the  shell  are  more  nearly  those  of  S. 
hannibalensis,  but  it  is  a  much  smaller  and  proportionally  shorter  species 
than  that. 

Horizon.— Kinderhook. 

Syringothyris  bushbergensis  n.  sp. 
Plate  LXXIII,  Figs.  8-10 

Description. — Shell  above  medium  size,  wider  than  long,  the  greatest 
width  near  or  on  the  hinge-line,  the  cardinal  extremities  rounded  or  sub- 
rectangular.     The  dimensions  of  a  large  pedicle  valve  are:  length  from 

l  9th  Ann.  Rep.  N.  Y.  State  Geol.,  p.  33.     (1890.) 


H92  MIKKISKIIM'IAN    KK.U'l  IIOl'ODA 

beak  to  front  margin  28  mm.,  height  of  cardinal  area  24  mm.,  greatest 
width  40  mm.,  length  of  hinge-line  36.8  mm.,  width  of  sinus  in  front  14 
nun .,  width  id'  deltliyriiini  ;it  hinge-line  10.5  mm. 

Pedicle  valve  subpyramidal  in  l'orin,  the  surface  sloping  IV the  umbo 

to  the  lateral  and  anterior  margins  with  a  gently  convex  curvature,  the 
surface  of  the  Lateral  slopes  rounding  towards  the  lateral  margins  of  the 
cardinal  area  ;is  they  approach  the  cardinal  extremities,  but  distinctly 
differentiated  from  the  area;  mesial  sinus  noil-plicate,  shallow,  rounded 
in  the  bottom,  narrow  and  sharply  defined  at  the  beak,  becoming  broad 
and  less  sharply  defined  anteriorly;  beak  erect;  cardinal  area  flat,  sloping 
anteriorly  from  the  hinge-line  at  an  angle  of  about  40  degrees  to  the 
plane  of  the  valve,  the  lateral  margins  sharply  defined;  delthyrium  nar- 
rowly triangular,  its  height  twice  or  more  than  twice  its  width  at  the 
base;  each  lateral  slope  marked  by  14  or  more  simple,  depressed,  radiat- 
ing plications  which  originate  near  the  cardinal  margin  and  beeome  faint 
or  nearly  obsolete  towards  the  cardinal  extremities  where  the  surface 
curves  towards  the  cardinal  area.  Internally  the  dental  lamellae  are 
rather  short  and  somewhat  thickened,  their  divergence  being  a  little 
greater  than  that  of  the  sides  of  the  mesial  sinus ;  the  muscular  scars  are 
rather  strongly  impressed  in  the  older  specimens,  and  are  short,  subovate 
in  outline,  with  a  distinct,  median,  longitudinal  ridge ;  the  delthyrial 
plate  extends  less  than  half  way  from  the  apex  of  the  delthyrium  to  the 
hinge-line,  it  is  convex  transversely  on  its  outer  surface  or  is  marked  by  a 
rather  broad,  rounded,  median,  longitudinal  elevation  whose  sides  slope 
to  the  lateral  margins  of  the  plates,  the  free  extension  of  the  syrinx  is 
apparently  short. 

The  minute  surface  markings  of  the  shell  are  not  capable  of  preserva- 
tion in  the  medium  in  which  the  specimens  occur,  but  a  few  inconspicuous, 
concentric  lines  of  growth  are  present  upon  most  of  the  specimens. 

Remarks. — This  species  is  established  upon  several  specimens  of  pedicle 
valves  preserved  as  internal  casts  and  external  moulds  in  a  friable  sand- 
stone. It  resembles  S.  extenuatus  in  some  respects,  but  has  a  greater  angle 
between  the  cardinal  area  and  the  plane  of  the  valve,  a  relatively  higher 
area,  and  the  cardinal  extremities  are  nearly  rectangular  or  rounded  in- 
stead of  extending  into  acutely  angular  points.  It  differs  from  S.  platy- 
pleurus  in  its  somewhat  lower  cardinal  area  and  the  rounded  or  quadrangular 
cardinal  extremities,  and  in  the  broad,  transverse  convexity  of  the  del- 
thyrial plate  instead  of  the  subquadrangular,  elevated,  longitudinal, 
median  rib.  It  is  not  at  all  similar  to  any  of  the  other  species  with 
flat  cardinal  area  and  can  be  distinguished  from  others  by  the  proportions 
and  flatness  of  the  cardinal  area. 

Horizon. — Bushberg  sandstone  of  the  Kinderhook. 


SYRINGOTHYRIS  393 

Syringothyris  Missouri  Hall 
Plate  LXX,  Figs.  6-15 

1894.  Syringothyris  Missouri  Hall,    13th    Ann.    Rep.  N.  Y.  State  Geol., 

p.  650. 

1895.  Syringothyris  Missouri  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

p.  363,  pi,  39,  figs.  29-31. 
1897.     Syringothyris  Missouri  Hall,  14th  Ann.  Rep.  N.  Y.  State  Geol.,  p. 
358,  pi.  8,  figs.  14-16. 

Description.— Shell  small,  with  very  high  cardinal  area,  wider  than  long, 
the  greatest  width  a  little  in  front  of  the  hinge-line,  the  cardinal  extremi- 
ties rounded.  The  dimensions  of  two  specimens,  the  larger  one  the  holo- 
type  of  the  species,  are :  length  of  pedicle  valve  from  beak  to  front  margin 
14.8  mm.  and  13.5  mm.,  length  of  brachial  valve  11.5  mm.  and  10.9  mm., 
height  of  cardinal  area  10  mm.  and  9  mm.,  maximum  width  of  shell  20 
mm.  and  18.5  mm.,  length  of  hinge-line  17  mm.  and  14  mm.,  thickness  15 
mm.  and  13.5  mm.,  width  of  sinus  in  front  6  mm.  and  5.2  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  steeply  from 
the  umbo  to  the  lateral  and  anterior  margins  with  a  slightly  convex  curve 
or  with  almost  no  curvature ;  the  mesial  sinus  originating  at  the  beak, 
shallow,  non-plicate,  rounded  in  the  bottom,  and  rather  sharply  defined, 
produced  in  front  in  a  short,  rounded  extension ;  beak  small,  a  little 
curved;  cardinal  area  very  high,  nearly  flat,  except  close  to  the  apex 
where  it  is  a  little  arched,  the  lateral  margins  ill-defined,  the  surface 
rounding  into  the  lateral  slopes;  delthyrium  narrowly  triangular,  much 
higher  than  wide,  the  point  of  the  syrinx  extending  two-thirds  the  dis- 
tance from  the  apex  to  the  hinge-line ;  each  lateral  slope  marked  by  from 
eight  to  ten  simple,  depressed,  radiating  plications  which  grow  succes- 
sively smaller  towards  the  cardinal  extremities.  Internally  the  dental 
plates  are  thin  and  well-developed,  sometimes  extending  nearly  half-way 
from  the  beak  to  the  front  margin  along  the  floor  of  the  valve ;  the  char- 
acter of  the  muscular  scars  is  not  clear  in  any  of  the  specimens  studied ; 
the  outer  surface  of  the  transverse,  syrinx-bearing  plate,  between  the 
dental  lamella?  is  distinctly  marked  by  a  longitudinal  median  rib  which 
is  extended  in  the  free,  spine-like  portion  of  the  syrinx  towards  the  hinge- 
line. 

Brachial  valve  moderately  convex,  a  little  compressed  towards  the  car- 
dinal extremities,  the  surface  curving  more  abruptly  to  the  cardinal  mar- 
gin ;  mesial  fold  originating  at  the  beak,  low,  rounded  on  top,  sharply 
defined ;  beak  short,  extending  a  little  beyond  the  hinge-line,  incurved ; 
the  cardinal  area  very  narrow. 

External  surface  of  the  shell  not  preserved  on  any  of  the  specimens 
examined,  but  the  surface  of  the  exfoliated  shells  shows  that  the  shell 
substance  was  punctate. 


:!!I4  MISSISSII'IMAN   BBACHIOPODA 

Remarks.— This  is  the  smallest  of  our  species  of  Syringothyris  and  is 
characterized  by  its  relatively  high  and  nearly  flat  cardinal  area,  whose 
surface  rounds  into  the  lateral  slopes  of  the  valve  without  any  sharp  line 
of  demarcation.  The  anterior  extension  of  the  dental  plates  of  the 
pedicle  valve  to  nearly  the  middle  of  the  valve  is  another  somewhat  un- 
usual character 

Horizon. — Chouteau  limestone  of  the  Kinderhook. 

Sykincotiivhis  NEWARKENSIS  n.  sp. 
Plate  LXVlil,  Figs.  8-15 

Description. — Shell  above  medium  size,  greatest  width  along  the  hinge- 
line  which  is  usually  greatly  extended,  the  cardinal  extremities  acutely 
angular.  The  dimensions  of  a  partially  restored  specimen  are:  length  of 
pedicle  valve  31  mm.,  length  of  brachial  valve  19  mm.,  greatest  width 
±58  mm.,  thickness  30.5  mm.,  height  of  cardinal  area  23  mm.,  width  of 
sinus  in  front  13  mm.,  width  of  delthyrium  at  base  10  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  with  a  gently 
convex  curvature  from  the  umbo  to  the  lateral  and  anterior  margins,  or 
sometimes  slightly  concave  from  the  umbo  to  the  cardinal  extremities; 
mesial  sinus  non-plicate,  originating  at  the  beak,  of  moderate  width  and 
depth,  rounded  in  the  bottom,  a  little  produced  in  front  in  a  rounded  ex- 
tension; beak  pointed,  a  little  incurved;  cardinal  area  high,  gently  con- 
cave with  the  curvature  increasing  towards  the  beak,  the  lateral  margins 
sharply  defined,  the  surface  sloping  anteriorly  from  the  hinge-line,  the 
lower  and  flatter  portion  lying  at  an  angle  of  about  60  degrees  to  the 
plane  of  the  valve ;  the  vertically  marked  secondary  area  well  defined 
when  the  surface  of  the  shell  is  well  preserved,  each  section  at  the  cardinal 
margin  being  about  equal  to  the  width  of  the  delthyrium  at  its  base ; 
delthyrium  rather  narrow,  its  width  at  the  base  being  about  two-fifths 
its  height.  Surface  of  each  lateral  slope  marked  by  from  18  to  20  simple, 
depressed,  radiating  plications,  which  originate  along  the  cardinal  margin, 
growing  successively  smaller  towards  the  cardinal  extremities.  Inter- 
nally the  dental  lamelke  extend  anteriorly  from  the  beak  for  somewhat 
more  than  one-third  the  length  of  the  valve ;  the  delthyrial  plate  is  mod- 
erately depressed  below  the  surface  of  the  cardinal  area  and  is  marked  by 
a  distinct  longitudinal  rib  which  is  produced  notably  beyond  the  margin 
of  the  plate  as  a  free  extension  of  the  syrinx. 

Brachial  valve  emarginate  in  front,  most  convex  between  the  middle 
and  the  anterior  margin  on  the  median  line,  the  surface  curving  more  ab- 
ruptly to  the  cardinal  margin,  compressed  towards  the  cardinal  extremi- 
ties ;  mesial  fold  well  developed,  originating  at  the  beak,  non-plicate, 
rounded  or  slightly  flattened  on  top ;  beak  short  and  somewhat  incurved, 
projecting  a  little  beyond  the  cardinal  margin.     Surface  of  each  lateral 


SYRINGOTIIYRIS  395 

slope  marked  by  simple,  depressed,  rounded,  radiating  plications,  similar 
in  number  to  those  of  the  opposite  valve,  but  marked  off  by  more  strongly 
impressed  radiating  furrows. 

The  minute  surface  markings  of  the  shell  are  not  well  preserved  upon 
any  specimen  observed,  hut  the  characteristic  markings  of  the  genus  are 
suggested  at  several  points,  and  the  punctate  structure  of  the  shell  is 
clearly  shown. 

Remarks. — This  species  is  perhaps  most  closely  related  to  S.  typa,  but 
it  is  a  smaller  shell,  more  extended  along  its  cardinal  line  in  its  normal 
condition,  with  relatively  much  shorter  brachial  valve  which  is  much 
more  compressed  towards  the  cardinal  extremities.  In  the  pedicle  valve 
the  delthyrium  is  much  more  narrowly  triangular  than  in  S.  typa,  and  the 
mesial  sinus  is  narrower.  One  specimen  studied  is  less  extended  along 
the  hinge-line  than  usual,  and  has  more  nearly  the  form  of  S.  typa,  but  it 
is  a  distorted  example,  showing  that  it  must  have  lived  under  abnormal 
conditions,  but  even  this  specimen  has  a  much  more  narrowly  triangular 
delthyrium  and  is  more  compressed  towards  the  cardinal  extremities  of 
the  brachial  valve  than  S.  typa.  Two  other  species  of  the  genus  which 
have  essentially  the  same  angle  of  divergence  between  the  cardinal  area 
find  the  plane  of  the  valve,  are  S.  hannibalensis  and  »SY.  halli,  but  each  of 
these  species  has  a  proportionally  lower  cardinal  area  and  a  more  broadly 
triangular  delthyrium. 

Horizon. — Kinderhook. 

Syringothyris  typus  Winched 
Plate  LXIX,  Figs.  1-5 

1863.     Syringothyris  typa  Winched,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  7. 
1886.     Syringothyris  typus  Winched,  Geological  Studies    or    Elements    of 

Geology,  p.  236,  figs.  181-182. 
1890.     Syringothyris  Carteri  Schuehert,  9th  Ann.  Rep.  N.  Y.  State  Geol., 

p.  30  (in  part). 

1894.  Syringothyris  tijpa  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pi.  30,  figs.  1-2. 

1895.  Syringothyris  typa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  26. 

figs.  6,  7,  10;  pi.  27,  figs.  1-3. 

Description. — Shell  large,  broader  than  long,  the  greatest  width  along 
the  hinge-line,  the  cardinal  extremities  angular.  The  dimensions  of  a 
nearly  complete  but  somewhat  distorted  specimen  are :  length  of  pedicle 
valve  from  beak  to  front  47  mm.,  length  of  brachial  valve,  approximately 
40  mm.,  width  along  hinge-line  68.5  mm.,  height  of  cardinal  area  26  mm., 
thickness  approximately  42  mm.,  width  of  sinus  in  front  28  mm.,  width 
of  delthyrium  at  base  16  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  with  a  gently 
convex  curvature  from  the  umbo  to  the  lateral  and  anterior  margins; 
mesial  sinus  non-plicate,  originating  at  the  beak  where  it  is  rather  well 


396  MISSISSIPPIAN  BKACI1I0P0DA 

defined,  becoming  broader  and  less  well  denned  toward  the  front,  rounded 
in  the  bottom  and  produced  anteriorly  in  a  moderately  long,  rounded, 
lingual  extension;  beak  pointed,  a  little  incurved;  cardinal  area  high, 
gently  concave  with  the  curvature  increasing  towards  the  beak,  sloping 
anteriorly  from  the  hinge-line  so  that  the  lower  and  flatter  portion  lies 
at  an  angle  of  about  55  degrees  1o  the  plane  of  the  valve  in  the  specimen 
whose  dimensions  are  inven  above,  the  triangular,  differentiated,  verti- 
cally marked  portion  of  the  area  lying  on  each  side  of  the  delthyrium  is 
Large,  the  Lateral  basal  angles  of  this  larger  triangle  lying  nearly  half  way 
from  the  basaL  angles  of  the  delthyrium  to  the  cardinal  extremities ; 
delthyrium  rather  broad,  its  width  between  two-thirds  and  one-half  its 
height;  each  lateral  slope  is  marked  by  from  20  to  24  simple,  depressed 
plications  which  originate  along  the  cardinal  margin  and  grow  suc- 
cessively smaller  towards  the  cardinal  extremities,  the  last  two  or  three 
or  more  being  almost  obsolete.  Internally  the  length  of  the  dental 
lamellae  in  the  bottom  of  the  valve  but  has  not  been  observed,  the  delthyrial 
plate  is  concave  transversely  with  a  slight,  median,  longitudinal  ridge, 
and  extends  about  half  way  from  the  apex  of  the  delthyrium  to  the  hinge- 
line,  the  free  extension  of  the  syrinx  is  rather  broad  and  is  about  one- 
third  the  length  of  the  fixed  delthyrial  plate. 

Brachial  valve  most  convex  on  the  mesial  line  at  or  near  the  anterior 
margin,  the  surface  curving  most  abruptly  to  the  cardinal  margin,  some- 
what impressed  towards  the  cardinal  extremities;  mesial  fold  well  de- 
veloped, rounded  on  top,  non-plicate;  beak  short,  incurved,  projecting 
slightly  beyond  the  cardinal  margin ;  cardinal  area  narrow,  lying  in  nearly 
the  plane  of  the  valve ;  each  lateral  slope  marked  by  simple,  rounded 
plications,  similar  in  number  to  those  of  the  opposite  valve  but  more 
strongly  developed. 

The  minute  surface  markings  of  the  shell  are  not  shown  on  the 
partially  exfoliated  specimens  examined,  but  a  few  small  patches  are 
sufficiently  well  preserved  to  show  that  the  characteristic  "twilled 
cloth"  markings  were  present.  Concentric  lines  of  growth  of  greater 
or  less  strength  are  commonly  distributed  irregularly  upon  both  valves. 
Shell  structure  minutely  punctate. 

Remarks.— This  species,  the  type  of  the  genus,  has  sometimes  been 
considered  as  a  synonym  of  S.  carteri,  a  species  which  is  imperfectly 
known,  the  types  of  that  species  being  brachial  valves  which  do  not  ex- 
hibit the  specific  or  even  the  generic  characters. 

Two  groups  of  spiriferoid  shells  with  greatly  elevated  cardinal  areas 
are  present  in  the  Mississippian  faunas,  both  of  which  are  characterized 
by  the  peculiar  "twilled  cloth"  surface  markings,  the  punctate  shell 
structure  and  usually  by  the  non-plicate  fold  and  sinus.  The  distinction 
between  the  two  groups  is  found  in  the  presence  or  absence  of  the  syrinx 


SYRINGOTHYRIS  397 

upon  the  transverse  delthyrial  plate  joining  the  dental  lamellie.  The 
group  of  shells  from  which  the  syrinx  is  lacking  includes  several  distinct 
specific  forms  from  various  horizons,  and  is  described  as  a  new  genus 
(Pseudosyrinx)  in  the  present  report.  Among  the  Waverly  specimens 
commonly  referred  to  S.  carteri,  examples  preserving  the  delthyrial  char- 
acters are  rare,  but  among  them  both  syrinx-bearing  shells  and  others 
withoiit  the  syrinx  have  been  observed,  and  as  it  seems  to  be  impossible 
to  determine  surely  what  8.  carteri  really  is,  the  name  should  be  dropped. 
S.  typa  differs  from  S.  hannibalensis  in  its  larger  size,  its  proportionally 
higher  cardinal  area,  in  its  more  deeply  placed  and  transversely  concave 
delthyrial  plate,  and  much  longer  free  extension  of  the  syrinx.  From  the 
European  8.  cuspidatus  with  which  it  has  sometimes  been  compared,  S 
typa  differs  in  its  lower  cardinal  area,  which  is  concave  instead  of  more 
or  less  strongly  convex,  in  the  symmetrical  or  nearly  symmetrical  beak 
of  the  pedicle  valve  instead  of  the  more  or  less  strongly  twisted  beak  of 
8.  cuspidatus,  and  in  the  very  different  condition  of  the  syrinx,  the  free 
portion  of  which  is  exceedingly  elongate  and  slender  in  the  European 
species. 

Horizon. — Upper  Kinderhook. 

Syringothyris  platypleurus  n.  sp. 
Plate  LXXII,  Figs.  1-4 

Description. — Shell  rather  large,  wider  than  long,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  acutely  angular.  The  di- 
mensions of  the  holotype  are :  length  of  pedicle  valve  from  beak  to  front 
34.5  mm.,  length  of  brachial  valve  23  mm.,  width  60  mm.,  height  of  car- 
dinal area  38.5  mm.,  thickness  41.8  mm.,  width  of  sinus  in  front  17  mm., 
width  of  delthyrium  at  hinge-line  13  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  in  nearly 
straight  lines  to  the  cardinal  extremities,  the  lateral  and  anterior  mar- 
gins slightly  compressed  vertically  towards  the  cardinal  extremities ; 
mesial  sinus  shallow,  rounded  in  the  bottom,  not  sharply  defined ;  the  beak 
erect,  pointed ;  cardinal  area  very  high,  nearly  flat,  its  lateral  margins 
sharply  defined,  sloping  anteriorly  from  hinge-line  at  an  angle  of  about 
40  degrees  to  the  plane  of  the  valve,  the  triangular,  vertically  marked, 
differentiated  region  lying  on  each  side  of  the  delthyrium  with  a  width 
at  its  base  a  little  less  than  one-half  the  length  of  the  hinge-line ;  delthy- 
rium narrowly  triangular,  nearly  three  times  as  high  as  wide ;  each  lateral 
slope  marked  by  about  20  rather  faint,  depressed  plications  which  orig- 
inate along  the  cardinal  margin  and  grow  successively  smaller  towards 
the  cardinal  extremities.  Internally  the  dental  lamellre  extend  more 
than  half  way  from  the  beak  to  the  anterior  margin  at  the  sides  of  the 
sinus  along  the  floor  of  the  valve,  their  angle  of  divergence  being  essen- 


398  MISSISSIIM'IAN    BRACHIOPODA 

tially  the  same  as  the  lateral  boundaries  of  the  sinus;  the  transverse  del- 
lliyrial  plate  extends  aboul  two-fifths  the  distance  from  the  apex  of  the 
delthyrium  to  the  hinge-line,  with  the  slender,  free  extension  of  the  syrinx 
continuing  at  least  one-hall'  as  Ear  again,  on  its  outer  side  the  delthyrial 
plate  is  tia t  on  either  side,  with  a  narrow,  squarely  elevated  median, 
longitudinal  ridge,  which  continues  into  the  free  portion  of  the  syrinx; 
the  muscular  scars  are  narrow  and  not,  deeply  impressed,  and  are  divided 
longitudinally  by  a  slight  median  ridge. 

Brachial  valve  moderately  convex,  suhsemicircular  in  outline,  with  a 
regularly  rounded  emargination  in  front  occupying  the  width  of  the 
mesial  fold,  the  surface  curving  more  abruptly  to  the  cardinal  margin, 
compressed  towards  the  cardinal  extremities;  mesial  fold  of  moderate 
height,  rounded  on  top,  well  defined  towards  the  beak,  becoming  less 
well  defined  anteriorly  ;  each  Lateral  slope  marked  by  about  20  simple,  de- 
pressed, rounded,  radiating  plications,  similar  to  those  of  the  opposite 
valve  but  more  strongly  defined.  Internally  the  muscular  scars  are  not 
strongly  impressed,  they  are  divided  longitudinally  by  a  low  median  ridge 
which  extends  more  than  half  way  from  the  beak  to  the  anterior  margin. 

The  minute  surface  markings  and  punctate  shell  structure  are  not  pre- 
served upon  the  holotype  of  this  species,  this  specimen  being  for  the  most 
part  an  internal  cast,  the  parts  of  the  shell  which  are  preserved  being 
entirely  silicified  and  not  preserving  their  markings.  Several  concentric 
lines  of  growth  are  shown  upon  the  specimen. 

Remarks. — This  species  is  characterized  by  its  proportionally  high  area 
and  the  very  oblique  anterior  slope  of  the  area  from  the  hinge-line.  In 
the  small  angle  between  the  cardinal  area  and  the  plane  of  the  valve,  in 
the  shortness  of  the  pedicle  valve  from  beak  to  front  as  compared  with 
the  height  of  the  cardinal  area,  and  in  the  slight  vertical  compression  of 
the  pedicle  valve  towards  the  cardinal  extremities,  this  species  resembles 
8.  extewuatus.  It  is  fundamentally  different  from  S.  extenuatus,  however, 
in  its  proportionally  much  higher  cardinal  area  and  in  the  form  of  the 
delthyrial  plate  and  syrinx.  The  species  differs  from  8.  typa  in  its  flat 
and  more  posteriorly  sloping  cardinal  area,  and  in  the  form  of  the  del- 
thyrial plate  and  syrinx.  In  some  respects  this  shell  approaches  more 
closely  to  the  European  S.  enspidatus  than  any  other  of  the  American 
species,  the  flat  delthyrial  plate  with  its  squarish,  median,  longitudinal 
ridge  externally,  which  is  produced  in  the  slender  free  syrinx,  being 
similar  in  the  two  species,  but  the  free  syrinx  is  much  more  elongate  in 
8.  cuspidatus;  in  8.  platypleurus,  however,  the  cardinal  area  is  not  convex, 
the  beak  is  not  distorted,  and  the  anterior  slope  of  the  area  is  much 
greater. 

A  specimen  from  the  lower  Burlington  limestone  at  Osceola,  Missouri, 
has  been  referred  to  this  species.     It  shows  only  a  portion  of  the  in- 


SYRINGOTHYRIS  399 

ternal  surface  of  the  cardinal  area,  including  a  considerable  portion  of 
the  delthyrial  plate  with  the  syrinx  well  preserved.  This  specimen  had 
a  very  high  and  flat  cardinal  area  with  a  narrowly  triangular  delthyrium, 
the  proportions  sc  far  as  preserved  being  essentially  the  same  as  in  the 
type  of  S.  platypleurus,  the  only  important  difference  between  it  and  the 
type  of  the  species,  so  far  as  can  be  seen,  is  in  the  apparently  perfectly 
flat  external  surface  of  the  delthyrial  plate,  the  longitudinal,  squarish 
ridge  being  absent. 

A  small  specimen  from  Louisiana,  Missouri,  with  an  approximate  width 
of  28  mm.  along  the  hinge-line,  when  completed,  agrees  well  with  the  type 
of  the  species  in  the  slope  of  the  cardinal  area  and  in  the  characters  of 
the  delthyrial  plate,  but  the  area  is  proportionally  lower  and  is  very 
slightly  arched  just  under  the  beak,  the  number  of  plications  is  smaller, 
which  may  well  be  due  to  the  smaller  size  of  the  shell,  and  there  are  very 
faint  indications  of  several  obscure  plications  in  the  mesial  sinus.  This 
specimen  preserves  the  minute  surface  characters  which  consist  of  series 
of  minute  papillae  arranged  in  quincunx,  giving  the  surface  the  peculiar 
"twilled  cloth"  appearance  so  characteristic  of  the  genus,  and  the  punc- 
tate structure  of  the  shell  is  indicated. 

Horizon. — Burlington  limestone. 

Syringothyris  textus  (Hall) 
Plate  LXIX,  Figs.  6-9 ;  Plate  LXX,  Figs.  1-4 ;  Plate  LXXI,  Figs.  1-2 

1857.     Spirifer  textus  Hall,  10th  Rep.  X.  Y.  State  Cab.  Xat.  Hist,,  p.  169. 
1875.  Spirifer  Carteri  Meek,  Pal.  Ohio,  vol.  2,  p.  2S5.  pi.  14.  figs.  7a-d. 
1881.     Spirifer  textus  White,  2nd  Ann.  Rep.  Dep.  Stat,  and  Geol.  Ind.,  p. 

512,  pi.  7,  figs.  1-2. 
1890.     Syringothyris  texta  Schuchert,  9th   Ann.   Rep.  N.  Y.   State   Geol., 

p.  34. 
1894.     Syringothyris  texta  Hall  and  Clarke.  Int.  to  Study  of  Brack,  pt.  2, 

pi.  30,  figs.  4-9. 
1894.     Syringothyris  texta  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  88. 
1S95.     Syringothyris  texta  Hall  and  Clarke.  Pal.  X.  Y.,  vol.  8,  pt.  2.  pi. 

26,  figs,  9,  12  ;  pi.  27,  figs.  4-12. 

Description. — Shell  large,  much  broader  than  long,  the  greatest  width 
along  the  hinge-line,  the  cardinal  extremities  angular.  The  dimensions 
of  a  nearly  perfect  specimen  of  about  average  size  are :  length  of  pedicle 
valve  from  beak  to  front  margin  43.6  mm.,  length  of  brachial  valve  34.5 
mm.,  height  of  cardinal  area  28  mm.,  width  along  the  hinge-line  95  mm., 
thickness  43  mm.,  width  of  mesial  sinus  in  front  25  mm.,  width  of  delthy- 
rium at  hinge-line  18  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the  beak 
to  the  antero-lateral  margins  with  a  gently  convex  curve,  from  the  beak 
to  the  anterior  margin  along  the  median  line  the  slope  is  also  gently  con- 


400  MISSISSII-IMAN   BRACHIOPODA 

vex  but  is  much  more  abrupl  ;  mesial  sinus  non-plicate,  originating  at  the 
beak,  it  is  narrow  and  rather  sharply  defined  in  the  umbonal  region,  be- 
coming broader  and  less  sharply  defined  anteriorly,  deep  and  rounded  in 
the  bottom,  produced  in  front  in  a  rounded  lingual  extension;  beak  ob- 
tusely pointed,  usually  nearly  erect  but  sometimes  a  little  incurved;  car- 
dinal area  high  and  usually  nearly  flat,  sometimes  moderately  arched 
Inwards  the  beak,  the  entire  surface  in  those  specimens  with  a  flat  area, 
and  the  lower,  flatter  portion  in  those  becoming  concave  towards  the  beak, 
slopes  anteriorly  from  the  hinge-line  at  an  average  angle  of  58  degrees  in 
12  specimens,  the  lateral  margins  sharply  defined,  usually  sloping  from 
the  beak  to  the  cardinal  extremities  with  a  gently  convex  curvature  which 
becomes  a  little  more  abrupt  as  it  approaches  the  cardinal  extremities; 
delthyrium  huge,  broadly  triangular,  higher  than  wide,  covered  by  a 
pseudodeltidium  which  is  usually  destroyed ;  each  lateral  slope  marked 
by  from  18  to  24  simple,  depressed,  rounded  plications  which  originate 
along  the  cardinal  margin.  Internally  the  dental  plates  are  short  and 
rather  thick,  the  continuous  portion  of  the  transverse  syrinx-bearing 
plate  connecting  them  is  flat  externally  and  extends  one-third  or  less  than 
one-third  of  the  distance  from  the  beak  to  the  hinge-line,  with  the  free, 
median,  spine-like,  tubular  projection  sharply  differentiated  from  the 
apical  portion,  more  or  less  trifid  at  its  termination,  and  reaching  to  a 
point  beyond  the  middle  of  the  distance  from  the  beak  to  the  hinge-line; 
muscular  scars  strong  and  well-defined,  subovate  in  outline,  the  adductor 
scars  narrow  and  elongate,  occupying  a  rather  sharply  depressed  area 
along  the  median  line  of  the  valve,  the  diductor  scars  on  either  side 
much  larger  and  marked  by  numerous  branching  grooves  and  ridges 
which  tend  to  radiate  in  all  directions  from  the  lateral  margins  of  the 
adductor  scars. 

Brachial  valve  strongly  convex,  its  depth  sometimes  nearly  or  quite 
equal  to  that  of  the  pedicle  valve,  the  surface  convex  from  the  cardinal 
to  the  antero-lateral  and  anterior  margins,  with  the  curvature  more  ab- 
rupt to  the  cardinal  margin,  towards  the  cardinal  extremities  the  surface 
usually  becomes  somewhat  compressed;  the  rounded,  non-plicate  mesial 
sinus  is  depressed  towards  the  beak,  becoming  much  higher  and  less 
sharply  defined  anteriorly ;  cardinal  area  narrow  and  inconspicuous ;  beak 
short,  incurved,  but  little  extended  beyond  the  cardinal  margin;  the  pli- 
cations of  the  lateral  slopes  entirely  similar  to  those  of  the  opposite  valve 
and  alternate  with  them.  Internally  the  cardinal  process  is  broad  and 
flat,  with  a  short  median  thickening  of  the  interior  of  the  valve  in  front 
of  its  base,  its  surface  of  muscular  attachment  marked  by  numerous,  fine, 
vertical,  angular  grooves  and  ridges ;  the  crural  plates  are  thick  and 
strong,  with  rather  small  dental  sockets  excavated  in  their  outer  margins ; 
the  muscular  scars  large,  reaching  more  than  half-way  to    the    anterior 


SYRINGOTHYRIS  -401 

margin  of  the  valve,  not  deeply  impressed,  extending  laterally  beyond 
the  limits  of  the  mesial  fold  posteriorly,  but  confined  within  the  limits  of 
the  fold  anteriorly,  marked  by  a  slight  median  depression  which  is  some- 
times scarcely  noticeable. 

Remarks.  —  This  is  perhaps  the  best  known  species  of  Syringothyris,  being 
especially  abundant  in  some  of  the  Knobstone  beds  of  southern  Indiana. 
It  is  characterized  by  the  great  width  and  the  comparatively  low  and 
nearly  flat  cardinal  area,  Schuchert1  lias  considered  both  S.  subcuspidatus 
and  S.  propinquus  as  synonyms  of  S.  texta,  but  S.  sxibeuspidatus  is  certainly 
distinct  from  it  and  perhaps  also  S.  propinquus.  The  distinguishing  char- 
acteristics of  these  species  will  be  discussed  under  the  descriptions  of 
these  forms. 

Horizon.—  Keokuk  limestone  and  Knobstone  formation. 

Syringothyris  subcuspidatus  (Hall) 

Plate  LXXI,  Figs.  3-7 

1858.     Spirifer  subcuspidatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  646,  pi.  20, 
figs.  6a-b. 

1894.  Syringothyris  subcuspidata  Hall  and  Clarke,  Int.  to  Study  of  Brack., 

pt.  2,  pi.  30,  fig.  3. 

1895.  Syringothyris  subcuspidatus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8, 

pt.  2,  pi.  26,  figs.  8,  11;  pi.  27,  fig.  18. 

Description. — Shell  large,  wider  than  long,  the  greatest  width  at  the 
hinge-line,  the  cardinal  extremities  usually  sub-rectangular.  The  dimen- 
sions of  a  nearly  complete  specimen  are :  length  of  pedicle  valve  from 
beak  to  front  53.5  mm.,  length  of  brachial  valve  40.3  mm.,  width  66  mm., 
height  of  cardinal  area  18.6  mm.,  thickness  42  mm.,  width  of  sinus  in 
front  26.2  mm.,  width  of  delthyrium  at  base  12  mm. 

Pedicle  valve  strongly  convex,  most  prominent  on  the  umbo,  the  surface 
sloping  to  the  cardinal  extremities  with  a  gently  convex  curvature,  and 
with  a  greater  curvature  to  the  antero-lateral  and  anterior  margins ; 
mesial  sinus  of  moderate  depth,  rounded  in  the  bottom,  originating  at 
the  beak  where  it  is  narrow  and  sharply  defined,  becoming  broader  and 
less  sharply  defined  anteriorly,  produced  in  front  in  a  rounded  lingual 
extension ;  the  beak  nearly  erect  or  a  little  incurved,  sometimes  slightly 
unsymmetrical  or  twisted ;  cardinal  area  rather  high,  broadly  triangular, 
nearly  flat  or  gently  concave,  sloping  posteriorly  from  the  hinge-line,  the 
inferior  portion  lying  at  an  angle  of  about  95  degrees  to  the  plane  of  the 
valve,  the  differentiated,  vertically  marked  region  lying  on  either  side 
of  the  delthyrium  is  very  broad,  the  base  of  the  triangle  being  more  than 
one-half  of  the  total  length  of  the  hinge-line ;  delthyrium  broad,  its  width 

i  9th  Ann.  Rep.  N.  Y.  State  Geol.,  p.  34.     (1890.) 


402  MISSISSII'I'IAN     BKACIIHU'ODA 

at  the  base  being  two-thirds  or  more  of  the  height;  each  lateral  slope 
marked  by  from  18  to  20  simple,  depressed,  rounded  plications  which  are 
nearly  or  quite  as  strong  as  those  of  the  opposite  valve,  they  originate 
along  the  cardinal  margin  and  grow  successively  smaller  towards  the 
cardinal  extremities.  Internally  the  dental  lamellae  are  well  developed 
and  rather  thick,  they  extend  anteriorly  along  the  floor  of  the  valve  for 
nearly  one-half  the  distance  from  the  beak  to  the  antero-lateral  margins, 
diverging  from  the  beak  at  an  angle  much  greater  than  the  lateral 
margins  of  the  mesial  sinus ;  the  muscular  scars  large  and  broad,  reaching 
more  than  half  way  from  the  beak  to  the  front  of  the  shell,  divided 
along  the  median  line  from  the  beak  nearly  to  the  middle  of  the  scar  by  a 
low  median  ridge  or  septum;  the  delthyrial  plate  between  the  dental 
lamella1  reaches  about  half  way  from  the  apex  of  the  delthyrium  to  the 
hinge-line,  with  the  free  part  of  the  syrinx  extending  still  further  down- 
ward, it  is  distinctly  keeled  longitudinally  along  the  median  line,  the  keel 
extending  out  into  the  free  part  of  the  syrinx. 

Brachial  valve  sometimes  nearly  or  quite  as  convex  as  the  pedicle, 
its  greatest  convexity  on  the  median  line  at  the  front  of  the  valve,  the 
surface  curving  more  abruptly  to  the  cardinal  margin  and  becoming 
more  or  less  compressed  towards  the  cardinal  extremities;  mesial  fold 
sharply  defined  to  the  beak  where  it  is  narrow  and  scarcely  elevated  above 
the  general  surface  of  the  valve,  becoming  broader  and  higher  anteriorly 
and  rounded  on  top ;  beak  short,  incurved,  the  umbonal  region  projecting 
somewhat  beyond  the  cardinal  margin ;  cardinal  area  narrow,  lying  nearly 
in  the  plane  of  the  valve;  each  lateral  slope  marked  by  18  or  20  simple 
plications  similar  to,  but  sometimes  a  little  stronger  than,  those  of  the 
opposite  valve. 

The  minute  surface  markings  are  not  commonly  fully  preserved  upon 
the  more  or  less  exfoliated  specimens  of  this  species,  but  they  are  suffi- 
ciently well  preserved  in  patches  to  indicate  that  they  are  of  the  typical 
"twilled  cloth"  character  which  is  common  to  the  genus.  The  punctate 
structure  of  the  shell  is  also  commonly  obliterated  and  has  not  been 
observed  in  any  of  the  specimens  studied,  but  it  was  doubtless  present  in 
the  living  shell.  Concentric  lines  of  growth  are  commonly  present  upon 
the  shells,  they  are  irregularly  arranged  and  of  varying  strength,  some  of 
them  usually  being  conspicuous. 

Remarks.— This  species  has  been  considered  as  a  synonym  of  S.  textus  by 
Schuchert,1  but  the  two  forms  are  clearly  distinct  in  several  important  re- 
spects. 8.  subcuspidatus  is  commonly  a  narrower  shell  with  proportionally 
lower  cardinal  area,  which  is  usually  moderately  concave  instead  of  flat; 
a  more  important  difference  is  in  the  position  of  the  cardinal  area  which 
slopes  posteriorly  from  the  hinge-line,  making  an  obtuse  angle  with  the 

19th  Ann.  Rep.  N.  Y.  State  Geol.,  p.  34.     (1890.) 


SYRINGOTHYRIS  403 

plane  of  the  valve,  while  in  S.  textus  it  slopes  anteriorly  and  the  angle 
with  the  plane  of  the  valve  is  acute.  The  delthyrial  plate  in  this  species 
is  distinctly  keeled  longitudinally  while  in  8.  textus  it  is  nearly  or  quite 
fiat  upon  its  outer  surface.  The  species  resembles  8.  typa  in  the  broad 
and  large  muscular  impression  of  the  pedicle  valve  and  in  the  strong  pli- 
cations of  the  shell  which  are  more  nearly  equal  on  the  two  valves  than  in 
many  species  of  the  genus. 
Horizon.  —  Keokuk  limestone. 

SYRINGOTHYRIS  SOLIDIROSTRIS  n.  Sp. 

Plate  LXX,  Fig.  5 

Description. — Shell  large,  wider  than  long,  the  greatest  width  along  the 
hinge-line,  the  cardinal  extremities  angular.  The  type  specimens  are  too 
fragmentary  to  give  accurate  measurements,  but  one  incomplete  pedicle 
valve  has  the  following  dimensions:  maximum  length  from  beak  to  front 
margin  50.5  mm.,  maximum  width  along  hinge-line  57.5  mm.,  height  of 
cardinal  area  27  mm.,  width  of  delthyrium  at  hinge-line  18.5  mm. 

Pedicle  valve  obliquely  subpyramidal  in  form,  most  prominent  at  the 
umbo,  the  surface  sloping  to  the  cardinal  extremities,  the  lateral  and  an- 
terior margins  with  a  gently  convex  curvature ;  mesial  sinus  non-plicate, 
originating  at  the  beak,  rather  sharply  defined,  of  medium  depth  and 
rounded  in  the  bottom ;  the  beak  obtusely  pointed,  erect ;  cardinal  area 
nearly  flat,  inclined  posteriorly  from  the  hinge-line  at  an  angle  greater 
than  90  degrees  to  the  plane  of  the  valve,  and  increasing  with  the  age  of 
the  shell;  delthyrium  broad,  its  width  two-thirds  or  more  than  two-thirds 
the  height;  each  lateral  slope  of  the  valve  marked  by  about  18  strong, 
simple,  rounded  plications  which  originate  along  the  cardinal  margin  and 
grow  successively  smaller  towards  the  cardinal  extremities.  Internally 
the  rostral  portion  of  the  valve  is  nearly  solidified  back  of  the  delthyrial 
plate,  the  continuous  portion  of  the  delthyrial  plate  is  about  three-fourths 
as  long  from  the  apex  of  the  delthyrium  as  the  total  height  of  the  delthy- 
rium and  is  concave  transversely,  the  free  extension  of  the  syrinx  is  rela- 
tively short  and  broad,  and  is  attached  nearly  to  its  distal  extremity  to 
the  floor  of  the  valve ;  the  dental  lamella?  are  short  and  rather  thick  and 
diverge  much  more  widely  than  the  lateral  boundaries  of  the  mesial  sinus  ; 
the  muscular  scars  are  broad  and  deeply  impressed,  with  a  distinct, 
rounded,  mesial  elevation  corresponding  with  the  mesial  sinus  of  the  ex- 
ternal surface  of  the  valve. 

In  the  condition  of  preservation  of  the  type  specimens  the  minute  sur- 
face markings  and  punctate  shell  structure  are  obliterated.  Rather  strong 
concentric  lines  of  growth  are  present  which  are  distributed  across  the 
entire  shell,  but  become  somewhat  more  crowded  anteriorly. 

Remarks. — This  species  has  been  described  from  two  imperfect  pedicle 
valves,  the  brachial  valve  being  unknown.     It   is  characterized  by  the 


404  Mississil'l'lAN   BRACHIOPODA 

great  deposil  of  shelly  matter  at  the  beak  and  the  essential  solidification 
of  the  rostral  portion  of  the  valve;  by  the  broad  and  deep  muscular  im- 
pression; by  the  strong  plications  of  the  shell;  and  by  the  nearly  flat, 
posteriorly  sloping  cardinal  area.  The  pedicle  valve  illustrated  by  Hall 
and  Clarke.'  as  8.  SUbcuspida&US  is  evidently  an  example  of  this  species. 
This  species  differs  from  8.  SubcuspidatvA  in  its  flatter  cardinal  area,  its 
longer  and  transversely  concave  delthyrial  plate,  and  the  solidification 
of  the  rostral  portion  of  the  pedicle  valve. 
Horizon. — Keokuk  limestone. 

Genus  PSEUDOSYRINX  n.  gen. 

Description.— Shell  essentially  like  Syringothyris  in  its  outer  form  and 
proportions.  The  pedicle  valve  with  the  lateral  slopes  usually  rounding 
into  the  cardinal  area;  internally  the  dental  lamellas  are  elongate,  some- 
limes  reaching  to  or  past  the  middle  of  the  valve,  the  delthyrial  plate 
well  developed,  reaching  to  varying  distances  towards  the  cardinal  mar- 
gin of  the  valve,  its  free  margin  describing  a  concave,  curve ;  no  syrinx 
developed  upon  its  inner  surface.  The  surface  of  the  cardinal  area  dif- 
ferent ialed  into  three  regions  as  in  Syringothyris,  and  similarly  marked. 
Punctate  shell  structure  and  fine  textile  surface  markings  as  in  Syringo- 
thyris. 

Remarks.  —  The  genus  Pseudosyrinx  has  been  established  to  include  a 
group  of  spiriferoid  shells  with  high  cardinal  area,  punctate  shell  struc- 
ture, and  distinct  delthyrial  plate  which  differs  from  that  in  Syringothyris 
in  the  entire  absence  of  a  syrinx  upon  its  inner  surface.  The  various 
species  of  the  genus  have  commonly  been  referred  to  one  or  another  of  the 
species  of  Syringothyris,  but  a  careful  investigation  of  a  large  number  of 
specimens  has  led  to  the  firm  conviction  that  they  should  be  placed 
in  a  distinct  generic  group  differing  from  Spirifer  in  the  main  in  the  same 
manner  as  Syringothyris,  and  differing  from  Syringothyris  in  the  absence 
of  a  syrinx.  It  was  at  first  supposed  that  the  absence  of  a  syrinx  in  cer- 
tain examples  of  spiriferoid  shells  with  high  cardinal  area  was  accidental, 
but  upon  the  continued  occurrence  of  this  feature  in  specimens  preserved 
in  such  a  way  as  to  show  certainly  that  no  syrinx  had  ever  been  present, 
and  the  association  of  this  condition  with  other  characters  of  specific 
value,  such  as  size,  proportions  of  the  shell,  etc.,  the  conclusion  was  forced 
that  they  should  be  separated  under  a  new  generic  name.  Besides  the 
absence  of  the  syrinx  there  are  several  other  features  which  are  more 
commonly  present  in  Pseudosyrinx  than  in  Syringothyris ;  the  dental  lamella? 
are  commonly  continued  further  anteriorly  along  the  floor  of  the  pedicle 
valve  than  in  Syringothyris,  and  the  lateral  margins  of  the  cardinal  area 
are  more  commonly  marked  by  a  rounding  of  the  surface  of  the  area  into 

lPal.  N.  Y.,  vol.  8,  pt.  2,  pi.  26,  fig.  11.     (1894.) 


PSEUDOSYRINX  405 

the  lateral  slopes  of  the  valve,  than  in  Syringothyris.  The  little  shell  which 
has  been  described  as  Syringothyris  missouri  H.  &  C.  has  the  external  as- 
pects of  Pseudosyrinx,  the  long  dental  lamellae  and  the  rounded  lateral 
margins  of  the  cardinal  area,  and  were  it  not  for  the  fact  that  the  syrinx 
has  actually  been  observed  in  the  type  specimen,  the  species  would  be 
placed  in  this  new  genus.  P.  missouriensis,  described  in  this  report  as  a 
new  species,  is  designated  as  the  genotype  of  the  new  genus. 

Pseudosyrinx  differs  from  the  genus  recently  described  by  Kindle  as 
Syringospira,1  in  the  continued  divergence  of  the  dental  lamellae  through- 
out their  entire  length,  and  in  the  absence  of  plications  upon  the  fold  and 
sinus.  In  Kindle 's  genus  the  dental  lamellae  converge  anteriorly  so  as  to 
become  united  a  short  distance  in  front  of  the  apex  of  the  valve  and  form 
with  the  delthyrial  plate  a  subcorneal  or  tube-like  chamber  in  the  poste- 
rior portion  of  the  pedicle  valve,  with  its  opening  directed  towards  the 
opposite  valve. 

Pseudosyrinx  sampsoni  Weller 

Plate  LXVII,  Figs.  11-13 

1909.     Syringothyris  sampsoni  Weller,  'Bull.   Geol.   Soe.  Am.,  vol.  20,  p. 
311,  pi.  14,  fig.  4. 

Description. Shell  large,  wider  than  long,  the  greatest  width  at  or  near 
the  hinge-line,  the  cardinal  extremities  apparently  a  little  rounded  or  per- 
haps subangular.  The  dimensions  of  the  holotype,  a  somewhat  crushed 
specimen,  are :  length  of  pedicle  valve  from  beak  to  front,  approximately 
50  mm.,  length  of  brachial  valve  approximately  45  mm.,  greatest  width 
approximately  77  mm.,  length  of  hinge-line  approximately  74  mm.,  height 
of  cardinal  area  56  mm.,  width  of  delthyrium  at  base  16  mm.,  width  of 
sinus  in  front  approximately  28  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  steeply  from 
the  umbonal  region  to  the  lateral  and  anterior  margins ;  mesial  sinus  non- 
plicate,  of  moderate  depth,  rounded  in  the  bottom,  not  sharply  defined 
laterally,  produced  in  front  in  a  rounded  lingual  extension ;  beak  small, 
pointed,  slightly  incurved ;  cardinal  area  of  great  height,  nearly  flat  ex- 
cept just  under  the  beak  where  it  is  a  little  concave ;  it  slopes  anteriorly 
from  the  hinge-line  to  the  beak  in  the  type  specimen  at  an  angle  of  appar- 
ently 30  degrees,  although  this  may  be  too  small ;  the  lateral  margins  are 
not  well  preserved  in  the  type  but  they  apparently  round  rather  abruptly 
into  the  lateral  slopes  of  the  valve,  the  triangular,  vertically  marked  dif- 
ferentiated region  lying  on  each  side  of  the  delthyrium  has  a  width  of 
base  along  the  hinge-line  about  twice  that  of  the  base  of  the  delthyrium 
and  less  than  one-half  the  total  length  of  the  hinge-line ;  the  delthyrium 
is  narrowly  triangular,  its  height  being   about    three    times  its  width  at 

lBull.  U.  S.  Geol.  Survey,  No.  391,  p.  28.     (1909.) 


406  MISSISSII'I'IAN    BRACHIOPODA 

the  base;  each  lateral  slope  bearing  about  16  or  18  simple,  depressed, 
nearly  obsolete  radiating  plications  which  originate  along  the  cardinal 
margin  and  become  successively  Smaller  Inwards  the  cardinal  extremities. 
Internally  the  binge-teeth  are  supported  by  conspicuous,  slightly  diverg- 
ing, dental  lamellae  which  extend  beyond  the  middle  of  the  valve  along 
its  inner  surface,  their  divergence  being  much  less  than  that  of  the  lat- 
eral margins  of  the  mesial  sinus;  the  dclthyrial  plate  well  developed, 
transversely  concave,  reaching  about  half  way  from  the  beak  to  the  car- 
dinal margin. 

Brachial  valve  subsemicircular  in  outline,  with  a  broad,  rounded  emar- 
gination  in  front,  the  greatest  convexity  probably  near  or  at  the  front 
margin  on  the  mesial  line,  the  surface  curving  more  abruptly  to  the  car- 
dinal margin,  somewhat  compressed  towards  the  cardinal  extremities; 
mesial  fold  non-plicate,  rounded  on  top,  slightly  elevated  at  the  beak, 
becoming  broader  and  moderately  elevated  in  front;  beak  small,  incurved; 
plications  of  the  lateral  slopes  simple,  depressed,  rounded,  similar  to  those 
of  the  opposite  valve,  but  very  much  stronger. 

Surface  of  both  valves  marked  by  minute  papilla^  arranged  in  eoncen- 
trie  rows,  about  7  or  8  occupying  the  space  of  one  millimeter;  the  papillae 
of  successive  rows  are  alternate  in  position,  and  extending  anteriorly 
from  each  is  a  minute  groove  which  terminates  at  about  the  line  of  the 
next  succeeding  row  of  papillae,  taken  in  their  aggregate  the  grooves  give 
to  the  surface  the  appearance  of  being  covered  with  minute  shingles  with 
a  papilla  at  the  lower  extremity  of  each.  Concentric  lines  of  growth  of 
moderate  strength  occur  at  more  or  less  irregular  intervals  and  continue 
across  the  cardinal  area  of  the  pedicle  valve.     Shell  structure  punctate. 

Remarks.  —  This  species  most  closely  resembles  S.  gigas,  and  in  many  char- 
acters the  two  species  do  not  differ.  S.  sampsoni,  however,  has  a  propor- 
tionally higher  cardinal  area  and  more  narrowly  triangular  delthyrium, 
and  the  dental  lamellae  are  much  less  widely  divergent.  The  type  specimen 
is  a  badly  crushed  example  so  that  the  exact  angle  of  the  anterior  slope  of 
the  cardinal  area  cannot  be  determined,  but  it  is  apparently  somewhat 
smaller  than  that  in  8.  gigas.  The  shell  surface  has  been  largely  destroyed 
from  the  specimen,  but  where  it  is  preserved,  it  exhibits  the  typical 
"twilled  cloth"  ornamentation  of  this  genus  and  Syringotliyris. 

Horizon. — Fern  Glen  formation  and  Keokuk  limestone. 

PSEUDOSYRINX   MISSOURIENSIS   n.   Sp. 

Plate  LXV,  Figs.  5-9;  Plate  LXVI,  Figs.  11-1 ;? 

1894.     Syringotliyris  carteri  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  87,  pi.  40, 
fig.  10. 

Description. — Shell  above  medium  size,  broader  than  long,  the  greatest 
width  near  the  hinge-line,  the  cardinal  extremities  narrowly  rounded. 


PSEUDOSYRINX  407 

The  dimensions  of  an  incomplete  but  undistorted  specimen  are :  length  of 
pedicle  valve  from  beak  to  front  22  mm.,  length  of  brachial  valve  16  mm., 
width  38  mm.,  thickness  approximately  22.5  mm.,  height  of  cardinal  area 
17  mm.,  width  of  sinus  in  front  11.5  mm.,  width  of  deltbyrinm  at  base 
7.5  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  from  the  umbo 
to  the  lateral  and  anterior  margins  with  a  gently  convex  curve ;  the 
median  sinus  narrow  and  sharply  defined  at  the  beak,  rounded  in  the 
bottom,  of  moderate  depth,  becoming  broader  and  less  sharply  defined 
anteriorly ;  the  beak  small,  pointed,  slightly  curved  over  the  cardinal 
area ;  cardinal  area  nearly  flat  except  near  the  apex,  where  it  is  gently 
arched  just  beneath  the  beak,  the  lateral  margins  not  sharply  defined  but 
rounding  into  the  lateral  slopes  of  the  valve,  sloping  anteriorly  from  the 
hinge-line  at  an  angle  of  from  55  to  60  degrees  to  the  plane  of  the  valve, 
the  triangular,  vertically  marked,  differentiated  region  on  each  side  of 
the  delthyrium  is  rather  narrow,  the  base  of  the  triangle  upon  the  hinge- 
line  being  considerably  less  than  one-half  the  total  length  of  the  hinge- 
line;  delthyrium  narrowly  triangular,  the  height  nearly,  or  more  than 
twice,  the  width  at  the  base ;  each  lateral  slope  marked  by  from  16  to  18 
simple,  depressed,  radiating  plications  which  originate  along  the  cardinal 
margin  and  grow  successively  smaller  towards  the  cardinal  extremities. 
Internally,  the  dental  lamellae  are  well-developed,  and  extend  anteriorly 
along  the  floor  of  the  valve  more  than  half  way  from  the  beak  to  the 
front  margin,  their  divergence  being  the  same  as  that  of  the  sides  of  the 
median  sinus;  the  muscular  scars  are  narrow  and  not  deeply  impressed, 
with  a  low  longitudinal  ridge  dividing  them  along  the  median  line  ;  the 
delthyrial  plate  is  only  a  little  depressed  below  the  level  of  the  cardinal 
area,  and  reaches  less  than  half  way  from  the  apex  of  the  delthyrium  to 
the  hinge-line,  its  outer  surface  is  nearly  flat  or  slightly  convex  trans- 
versely, and  its  free  margin  is  a  regularly  concave  curve. 

Brachial  valve  much  shallower  than  the  pedicle,  subsemicircular  in  out- 
line, with  a  rounded  emargination  in  front  opposite  the  mesial  fold,  the 
surface  curving  more  abruptly  to  the  cardinal  margin  and  becoming 
somewhat  compressed  towards  the  cardinal  extremities ;  mesial  fold  of 
moderate  height,  rounded  on  top ;  each  lateral  slope  bearing  simple  pli- 
cations similar  to  those  of  the  opposite  valve  but  much  more  strongly 
defined. 

The  minute  surface  markings  of  both  valves  consist  of  very  fine  elongate 
papilbe  abruptly  raised  at  the  anterior  extremity  and  merging  into  the 
surface  of  the  shell  posteriorly,  these  papillae  are  arranged  in  concentric 
rows  and  alternate  with  each  other  in  position  in  succeeding  rows.  Shell 
substance  minutely  punctate.  Concentric  lines  of  growth  of  varying 
strength  occur  at  intervals  upon  both  valves  and  are  sometimes  crowded 
toward  the  front  margin. 


408  mississippian  brachiopoda 

li'<  marks. — This  species  has  been  described  in  the  main  from  specimens 
from  the  white  cherts  of  Lower  Burlington  age,  from  Louisiana,  Missouri. 
None  of  tin1  specimens,  from  this  locality,  which  have  heen  studied  are  com- 
plete, but  they  preserve  all  of  the  essential  characters  and  exhibit  the  fine 
surface  markings  in  a  most  perfect  manner.  Several  specimens  from  a 
similar  horizon  at  Osceola.  Missouri,  are  somewhat  larger,  the  largest 
one  having  a  width  along  the  hinge-line  of  about  60  mm.,  but  they  agree 
with  the  Louisiana  specimens  in  all  essentials  except  in  having  a  larger 
number  of  plications,  there  being  20  or  more  upon  each  lateral  slope,  a 
character  doubtless  due  to  the  larger  size  of  the  individuals.  The  species 
differs  from  S.  gigas  in  its  smaller  size,  its  greater  angle  between  the  car- 
dinal area  and  the  plane  of  the  valve,  and  in  the  more  rounded  lateral 
margins  of  the  area. 

The  shell  illustrated  by  Keyes  as  Syringothyris  carleri  is  certainly  a 
member  of  this  species,  although  it  is  proportionally  somewhat  wider 
along  the  hinge-line  and  consequently  has  a  relatively  lower  cardinal  area. 
It  has  the  rounded  lateral  margins  of  the  cardinal  area  of  this  species  and 
closely  resembles  none  of  the  species  of  Syringothyris. 

Horizon. — Burlington  limestone. 

PSEUDOSYRINX  KEOKUK   n.   Sp. 

Plate  LXVI,  Figs.  6-10;  Plate  LXVII,  Figs.  1-9 

Description.— Shell  of  about  medium  size,  broader  than  long,  the  great- 
est width  near  the  hinge-line,  the  cardinal  extremities  rounded.  The 
dimensions  of  a  nearly  complete  internal  cast  are :  length  of  pedicle  valve 
from  beak  to  front  margin  17  mm.,  length  of  brachial  valve  15  mm., 
width  28  mm.,  length  of  hinge-line  22.5  mm.,  thickness  41.1  mm.,  height 
of  cardinal  area  9.8  mm.,  Avidth  of  sinus  in  front  9.5  mm.,  width  of  delthy- 
rium  at  hinge-line  5.4  mm. 

Pedicle  valve  subpyramidal  in  form,  the  surface  sloping  in  nearly 
straight  lines  from  the  beak  to  the  lateral  extremities  and  with  a  gently 
convex  curvature  to  the  antero-lateral  and  anterior  margins ;  mesial  sinus 
of  moderate  depth,  rounded  in  the  bottom,  narrow  and  well  defined  at  the 
beak,  becoming  broader  and  less  sharply  defined  anteriorly,  produced  in 
front  in  a  rounded  lingual  extension ;  beak  small,  pointed,  a  little  curved ; 
cardinal  area  nearly  flat  below,  becoming  gently  concave  towards  the 
apex  just  under  the  beak,  sloping  anteriorly  from  the  hinge-line  at  an 
angle  of  about  55  degrees  to  the  plane  of  the  valve,  its  lateral  mar- 
gins rounding  regularly  into  the  surface  of  the  lateral  slopes  of  the 
valve,  the  vertically  marked,  differentiated,  triangular  region  lying  on 
either  side  of  the  delthyrium  has  a  width  along  the  base  of  the  triangle 
about  equal  to  one-half  the  length  of  the  hinge-line ;  delthyrium  narrowly 
triangular,  the  width  at  the  base  about  one-half  the  height;  each  lateral 


PSEUDOSYRINX  4-09 

slope  with  from  12  to  14  simple,  depressed,  radiating  plications  which 
originate  along  the  cardinal  margin  and  grow  successively  smaller  towards 
the  cardinal  extremities.  Internally  the  dental  lamellae  are  well  devel- 
oped and  extend  anteriorly  from  the  beak  along  the  floor  of  the  valve  for 
one-half  or  nearly  one-half  the  length  of  the  valve  to  the  anterior  margin 
on  either  side  of  the  sinus,  their  divergence  from  the  beak  is  a  little 
greater  than  the  divergence  of  the  lateral  margins  of  the  median  sinus ; 
the  muscular  scars  are  usually  faintly  impressed  and  are  either  not  divided 
longitudinally  by  a  median  ridge  or  by  a  very  slight  one ;  the  delthyrial 
plate  is  rather  short,  reaching  one-third  or  less  than  one-third  of  the 
distance  from  the  apex  of  the  delthyrium  to  the  hinge-line,  it  is 
nearly  flat  or  slightly  convex  transversely  with  a  regularly  concave  free 
margin. 

Brachial  valve  shallower  than  the  pedicle,  the  greatest  convexity  on 
the  median  line  at  or  near  the  front  margin,  the  surface  curving  more 
abruptly  to  the  cardinal  margin,  somewhat  compressed  towards  the  car- 
dinal extremities ;  the  mesial  fold  moderately  elevated,  rounded  on  top, 
well  defined  to  the  beak ;  the  beak  small,  projecting  a  little  beyond  the 
cardinal  margin,  a  little  incurved ;  cardinal  area  narrow  and  inconspicu- 
ous, lying  in  nearly  a  right  angle  to  the  area  of  the  opposite  valve.  In- 
ternally a  distinct  median  septum  extends  a  short  distance  forward  from 
the  beak  and  is  then  continued  to  about  the  middle  of  the  valve  as  a  slight 
median  ridge;  muscular  scars  obscure. 

The  minute  surface  markings  of  the  shell  are  not  well  shown  upon  any 
of  the  specimens  studied  because  of  their  condition  of  preservation,  but 
suggestions  of  the  "twilled  cloth"  form  of  ornamentation  is  recognizable 
upon  some  examples  in  patches ;  the  shell  structure  is  minutely  punctate, 
the  perforations  extending  also  across  the  cardinal  area  of  the  pedicle 
valve  to  the  border  of  the  central,  triangular,  differentiated  region  where 
they  stop  abruptly ;  concentric  lines  of  growth  of  varying  strength  are 
usually  present  at  irregular  intervals  upon  both  valves. 

Remarks. — This  species  is  the  smallest  member  of  the  genus  recognized 
in  our  faunas,  although  it  grows  to  a  larger  size  than  is  indicated  by  the 
dimensions  given,  the  largest  individual  which  has  been  referred  to  the 
species  having  a  width  of  46  mm.  This  largest  specimen  is  an  internal 
cast  of  a  pedicle  valve  in  chert,  and  differs  somewhat  from  the  smaller 
examples  in  having  longer  dental  lamella?  and  in  having  the  lingual  ex- 
tension of  the  sinus  of  greater  length,  but  both  these  characters  may  be 
due  to  the  greater  age  of  the  specimen.  The  holotype  of  the  species  is  a 
nearly  perfect  internal  cast  from  a  white  chert,  its  locality  is  not  given 
but  it  might  come  from  many  exposures  of  such  chert  in  the  Keokuk 
formation  of  the  Mississippi  valley.  The  punctate  structure  of  the  shell 
is  finely  shown  upon  it  as  upon  most  other  similar  chert  specimens,  by  the 


410  MISSISSII'PIAN   BRACHIOPODA 

siliceous   papilla'   which   cover  the  surface   of  the  specimens,   these   being 
the  casts  of  the  perforations  in  the  original  shell.     The  species  is  especi- 
ally characterized  by  its  small  size,  the  broadly  rounded  lateral  margins 
of  the  cardinal  area,  and  the  rounded  cardinal  extremities. 
Horizon. — Keokuk  limestone. 

PSEUDOSYRINX  GIGAS   n.  sp. 
PJate  LXV1,  Figs.  1-5 

Description. — Shell  large,  broader  than  long,  the  greatest  width  at  or 
near  the  hinge  line,  the  cardinal  extremities  suhangular  or  rounded.  The 
dimensions  of  a  nearly  complete  specimen  are:  length  of  pedicle  valve 
from  beak  to  front  50  mm.,  length  of  brachial  valve  38  mm.,  width  82 
mm.,  thickness  56  mm.,  height  of  cardinal  area  43  mm.,  width  of  sinus  in 
front  30  mm.,  width  of  delt hyrium  at  base  18  mm. 

Pedicle  valve  subpyra mida I  in  form,  the  surface  sloping  with  gentle 
curvature  from  the  umbonal  region  to  the  lateral  and  anterior  margins; 
the  mesial  sinus  non-plicate,  of  moderate  depth,  rounded  in  the  bottom 
and  ill-defined  laterally,  produced  anteriorly  in  a  broad,  rounded,  lingual 
extension;  beak  small,  pointed,  slightly  curved  over  the  cardinal  area; 
cardinal  area  very  high,  nearly  flat  from  the  hinge-line  to  a  point  near 
the  apex  where  it  is  gently  concave  for  a  short  distance  below  the  beak, 
it  slopes  anteriorly  from  the  hinge-line  at  an  angle  of  about  40  degrees 
to  the  plane  of  the  valve,  and  its  lateral  margins  round  rather 
abruptly  into  the  lateral  slopes  of  the  valve,  the  triangular,  vertically 
marked  differentiated  region  lying  on  each  side  of  the  delthyrium  is 
large,  the  base  of  this  larger  triangle  occupying  more  than  one-half 
the  total  length  of  the  hinge-line ;  delthyrium  narrowly  triangular,  the 
height  more  than  twice  the  width  ;  each  lateral  slope  bearing  about  16 
simple,  depressed,  often  ill-defined,  radiating  plications,  which  originate 
along  the  cardinal  margin  and  become  successively  smaller  towards  the 
cardinal  extremities.  Internally  the  hinge-teeth  are  supported  by  well- 
defined  dental  lamella1  which  are  continued  along  the  floor  of  the  valve 
for  nearly  or  quite  one-half  the  length  of  the  valve  from  the  beak  to  the 
front  margin,  their  divergence  anteriorly  being  about  equal  to  the  diverg- 
ence of  the  lateral  boundaries  of  the  mesial  sinus;  the  delthyrial  plate 
is  well  developed  and  extends  from  the  apex  of  the  delthyrium  to  a  point 
from  one-third  to  one-half  the  distance  to  the  hinge-line;  it  is  nearly  flat 
or  gently  convex  transversely  and  its  free  margin  is  a  regularly  concave 
curve. 

Brachial  valve  subsemicircular  in  outline,  with  a  deep,  broadly  rounded 
emargination  in  front  opposite  the  mesial  fold,  the  greatest  convexity  is 
on  the  median  line  at  the  front  margin,  the  surface  curves  more  abruptly 
to  the  cardinal  margin  and  is  somewhat  compressed  towards  the  cardinal 


PSEUDOSYRINX  411 

extremities,  the  iimbonal  region  is  rather  strongly  protuberant  beyond 
the  hinge-line;  the  mesial  fold  rounded  on  top,  sharply  defined  and  slightly 
elevated  at  the  beak,  becoming  broader  and  of  moderate  height  anteriorly ; 
the  beak  small,  broadly  pointed  and  rather  strongly  incurved ;  cardinal 
area  narrow,  concave,  lying  at  nearly  a  right  angle  to  the  area  of  the 
opposite  valve ;  plications  similar  in  number  to  those  of  the  opposite  valve 
but  much  more  sharply  defined. 

The  minute  surface  markings  consist  of  exceedingly  fine  radiating  stria1. 
Besides  these,  concentric  lines  of  growth  of  greater  or  less  strength  are 
present  which  are  often  crowded  at  intervals,  especially  towards  the 
front  of  the  shell. 

Remark*. — The  specimen  which  has  been  selected  as  the  holotype  of  this 
species  is  a  nearly  complete  silicified  specimen  whose  locality  is  unknown. 
Other  less  perfect  examples  from  Warsaw,  111.,  and  Crawfordsville,  Ind., 
have  been  studied.  The  species  is  characterized  by  its  large  size,  the 
nearly  flat  cardinal  area  which  becomes  arched  just  beneath  the  beak, 
and  by  the  small  angle  between  the  cardinal  area  and  the  plane  of  the 
valve.  Because  of  the  silicification  of  the  shell  the  minute  surface  mark- 
ings are  not  preserved  upon  the  type  specimen,  but  they  are  shown  on 
the  others  and  are  best  exhibited  upon  the  Warsaw  specimens.  Upon 
one  Crawfordsville  example  the  fine  radiating  stria3  appear  on  some 
parts  of  the  shell  to  be  interrupted  at  short  and  rather  regular  intervals, 
the  intervals  of  interruption  of  adjacent  strias  being  similar  along  con- 
centric lines,  the  striae  being  alternate  in  position  on  either  side  of  the 
lines  of  interruption.  This  arrangement  gives  to  the  surface  markings 
an  approach  to  the  "twilled  cloth"  markings  which  are  so  characteristic 
of  Syringothyris  and  of  at  least  some  of  the  species  of  this  genus. 

Besides  the  absence  of  a  syrinx,  this  species  differs  from  all  the  recog- 
nized species  of  Syringothyris  in  its  general  proportions,  and  can  not  be 
easily  confused  with  any  of  them.  There  is  a  strong  suspicion,  however, 
that  the  species  may  be  the  same  as  that  to  which  Troost1  gave  the  name 
Cyrtia  gigas.  His  description  is  entirely  inadequate  to  allow  the  recog- 
nition of  his  species  in  the  absence  of  the  type  or  of  authentic  specimens, 
but  the  proportions  of  the  cardinal  area  given  by  him  are  sufficiently  near 
those  of  the  specimen  used  for  the  definition  here  published,  although 
Troost 's  specimen  Avas  somewhat  larger.  In  order  to  avoid  confusion  in 
case  Troost 's  species  and  this  one  should  ever  be  proven  to  be  the  same, 
the  same  specific  name  has  been  used,  a  procedure  which  is  allowable, 
since  Troost's  species  has  only  been  referred  to  the  genera  Cyrtia  and 
Syringothyris. 

Horizon. — Keokuk  limestone. 

16th  Geol.  Rep.  Term.,  p.  12.     (1841.) 


412  MISSISSIPPIAN  BEACHIOPODA 

Genus  SPIRIFERELLA  Tschernyshew 

Description.  —  Shells  large  or  small,  both  valves  convex,  the  hinge-line 
shorter  than  the  greatest  width,  the  cardinal  extremities  rounded,  mesial 
sinus  in  the  pedicle  valve  and  fold  in  the  brachial  valve  well  developed 
and  without  plications,  or  only  slightly  plicated,  lateral  slopes  of  the 
valve  plicated.  The  pedicle  valve  with  a  moderately  high  cardinal  area 
whose  surface  rounds  into  the  lateral  slopes  of  the  valve;  internally  the 
denial  lamella'  are  very  strongly  developed  and  may  extend  anteriorly 
beyond  the  middle  of  the  valve;  they  are  joined  posteriorly  by  a  trans- 
verse delthyrial  plate  situated  a  little  beneath  the  level  of  the  general 
surface  of  the  cardinal  area;  the  muscular  scars  situated  between  the 
elongate  dental  lamella-  and  resembling  those  of  Spirifer.  Brachial  valve 
similar  to  that  of  Spirifer  with  a  slight  median  septum  internally.  Shell 
substance  punctate. 

Remarks. — These  shells  have  usually  been  included  in  the  genua  Spirifer, 
although  S.  plemis  has  sometimes  been  referred  to  Syringothyris.  In  none 
of  the  shells,  however,  is  there  any  suggestion  of  a  syrinx.  They  differ 
from  Spirifer  not  only  in  the  punctate  shell  structure,  but  in  the  exceed- 
ingly elongate  dental  lamellae,  and  are  really  more  closely  allied  to  those 
shells  that  have  been  placed  in  the  new  genus  Pseudosyrinx  in  this  report 
than  to  any  other.  They  differ  from  this  last  genus  in  their  much  more 
rotund  form,  in  their  much  less  elevated  and  more  arched  cardinal  area 
of  the  pedicle  valve,  in  their  shorter  hinge-line  and  in  the  more  extrava- 
gant development  of  the  dental  lamella?.  They  seem  certainly  to  be  con- 
generic with  the  shells  described  as  Spiriferella  clansi  by  Douville,1  al- 
though there  is  some  doubt  as  to  any  of  these  shells  being  certainly  con- 
generic with  Spiriferella  as  originally  described  by  Tschernyshew.2  For 
the  present,  however,  it  seems  better  to  refer  them  to  Spiriferella  than  to 
propose  a  new  generic  name  for  them. 

Spiriferella  plena  (Hall) 
Plate  LX1II,  Figs.  5-8 ;  Plate  LXIV,  Figs.  1-4 

1858.     Spirifer  plemis  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  603,  pi.  13,  figs. 

4a-d. 
1890.     Syringothyris  f  plena  Schuchert,  9th  Ann.  Rep.  N.  Y.  State  Geol., 

p.  37. 

1894.  Syringothyris  plena  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  88,  pi.  40, 

'%.  8. 

1895.  Spirifer  plemis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  37, 

figs.  32,  33. 
1909.     Spirifer  plemis  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  306. 

1  Bull.  Geol.  Soc.  France,  4th  ser.,  vol.  ix,  p.  153,  pi.  5,  figs.  3-5.     (1909.) 

2  Mem.  Cora.  Geol.  de  St.  Petersbourg,  vol.  2,  No.  2,  p.  513.     (1902.) 


SPIRIFERELLA  413 

Description.— Shell  large,  subglobose,  wider  than  long,  the  hinge-line  less 
than  the  greatest  width  of  the  shell,  the  cardinal  extremities  rounded. 
The  dimensions  of  a  nearly  perfect  individual  are :  length  56  mm.,  width 
70  mm.,  thickness  48  mm.,  length  of  hinge-line  51  mm.,  height  of  cardinal 
area  11.5  mm. 

Pedicle  valve  ventricose,  the  greatest  convexity  in  the  umbonal  region, 
the  surface  curving  abruptly  in  all  directions  from  the  umbonal  region 
but  most  abruptly  to  the  cardinal  margin,  the  convexity  of  the  valve  ex- 
tending out  to  the  cardinal  extremities;  the  beak  not  sharply  pointed,  a 
little  incurved ;  cardinal  area  rather  high,  arched,  the  inferior  portion 
making  an  angle  of  about  90  degrees  to  the  plane  of  the  valve,  the  curva- 
ture from  the  hinge-line  to  the  beak  describing  nearly  an  arc  of  a  circle, 
the  lateral  margins  not  sharply  defined  but  rounding  rather  abruptly  into 
the  lateral  slopes  of  the  valve,  the  delthyrium  large,  forming  nearly  an 
equilateral  triangle ;  lateral  slopes  of  the  valve  each  marked  with  from  16 
to  20  simple,  depressed,  rounded  plications,  the  smaller  of  which  towards 
the  cardinal  extremities  become  nearly  obsolete ;  mesial  sinus  narrow  and 
shallow  at  the  beak,  growing  rapidly  broader  towards  the  front,  of  mod- 
erate depth,  rounded  in  the  bottom,  without  plications,  in  full  grown 
examples  with  the  anterior  extremity  produced  into  a  broad,  lingual 
extension. 

Brachial  valve  as  convex  or  more  convex  than  the  pedicle,  its  greatest 
convexity  usually  at  the  anterior  margin,  the  convexity  extending  to  the 
cardinal  extremities  or  rarely  slightly  compressed  at  the  extremities ;  the 
beak  incurved  and  the  umbonal  region  projecting  beyond  the  hinge-line ; 
the  mesial  fold  without  plications,  scarcely  defined  at  the  beak,  becoming 
broad  and  high  and  rounded  anteriorly;  the  lateral  slopes  with  a  steep, 
convex  slope  from  the  margins  of  the  mesial  fold  to  the  margins  of  the 
valve,  the  slope  becoming  more  abrupt  to  the  cardinal  margin,  each  bear- 
ing plications  similar  in  form  and  number  to  those  upon  the  opposite  valve 
except  that  they  are  often  a  little  more  distinct. 

The  finer  surface  markings  consist  of  exceedingly  minute  papillae  or 
granulations  more  or  less  rhombic  in  outline,  with  the  longer  axis  longi- 
tudinal and  slightly  elevated  anteriorly,  arranged  in  more  or  less  definite 
diagonal  lines.  More  or  less  irregular  concentric  lines  of  growth  are 
usually  present  which  are  sometimes  crowded  towards  the  anterior 
margin. 

Internally  the  shell  is  characterized  by  the  exceedingly  elongate  dental 
lamella?  in  the  pedicle  valve,  which  extend  with  only  moderate  divergence 
nearly  or  quite  one-half  the  length  of  the  shell  from  the  beak  towards  the 
anterior  margin,  these  lamellae  are  thick  and  bifoliate,  splitting  readily 
along  their  median  plane ;  posteriorly  a  concave  transverse  plate  joins 
the  two  dental  lamellae  in  a   plane   a   little  depressed  below  the  general 


414  .mississiitian   BBACHIOPODA 

surface  of  the  cardinal  area,  this  plate  extends  from  the  beak  nearly  t<> 
the  binge-line,  its  cardinal  margin  being  concave. 

Remarks. — In  its  non-plicated  fold  and  sinus,  in  the  transverse  plate 
joining  the  posterior  portions  of  the  dental  lamellae,  and  in  the  minute 
surface  ornamentation  this  species  resembles  members  of  the  genus 
SyringothyHs,  to  which  genus  ii  1ms  sometimes  been  referred.  However. 
the  transverse  plate  in  the  delthyrium  does  not  bear  a  syrinx  upon  its 
anterior  surface  with  a  projecting  point  al  the  median  Line  towards  the 
hinge-line,  this  feature  of  the  shell  being'  in  essential  accord  with 
Pseudosyrinx.  A  similar  surface  ornamentation  is  not,  altogether 
lacking  in  the  genus  Hprrifcr,  as  several  Devonian  species  possess  it,  and  a 
similar  transverse  plate  is  also  developed  in  some  species  of  Spirifer,  al- 
though in  qo  other  is  it  known  to  be  so  conspicuously  developed  as  here. 
The  characters  which  differentiate  this  species  from  Pseudosyrinx  are  the 
rotund  form,  the  lower  and  more  arched  cardinal  area,  and  especially  the 
extravagant  development  of  the  dental  lamella?.  The  punctate  structure 
of  the  shell  is  not  commonly  well  preserved,  and  in  none  of  the  speci- 
mens examined  by  the  writer  has  it  certainly  been  seen.  Schuchert,1 
however,  says,  "shell  structure  distinctly  punctate,"  and  he  doubtless  ob- 
served it  in  specimens  more  favorably  preserved  than  any  of  those  ex- 
amined by  the  writer. 

Horizon. — Burlington  limestone. 

Spiriferella  latior  n.  sp. 
Plate  LXIII,  Figs.  9-10 

Description. — Shell  large,  broader  than  long,  the  hinge-line  shorter  than 
the  greatest  width,  the  cardinal  extremities  rounded.  The  dimensions 
of  a  nearly  complete  pedicle  valve  are:  length  about  45  mm.,  greatest  width 
about  68  mm.,  length  of  hinge-line  about  50  mm.,  height  of  cardinal  area 
16  mm. 

Pedicle  valve  strongly  convex,  the  greatest  depth  posterior  to  the 
middle  in  the  umbonal  region,  the  surface  curving  with  a  gentle  convexity 
from  the  umbo  to  the  anterior  and  antero-lateral  margins,  the  slope  from 
the  umbo  to  the  cardinal  extremities  being  a  little  concave;  the  beak 
pointed  and  moderately  incurved;  the  cardinal  area  large,  concave,  with 
the  curvature  increasing  a  little  towards  the  beak,  the  lateral  margins 
not  sharply  defined,  the  surface  rounding  into  that  of  the  lateral  slopes 
of  the  valve ;  the  delthyrium  very  large,  broadly  triangular ;  the  mesial 
sinus  originating  at  the  beak,  growing  very  broad  anteriorly,  rather 
shallow  and  regularly  rounded  in  the  bottom,  well  defined  laterally,  not 
marked  by  radiating  plications;  the  lateral  slopes  each  marked  by  from 

19th  Ann.  Rep.  N.  Y.  State  Geol.  for  1899,  p.  37.     (1890.) 


SPIKIFERELLA  415 

20  to  25  depressed,  rounded,  simple  plications  which  become  successively 
fainter  towards  the  cardinal  extremities,  the  last  four  or  five  often  being 
almost  obsolete.  Internally  the  dental  lamella'  are  remarkably  developed 
as  thick,  bifoliate  plates  extending  nearly  to  the  front  of  the  valve,  be- 
tween them,  in  the  posterior  portion  of  the  valve,  is  a  well  developed 
delthyrial  plate  rather  deeply  depressed  below  the  surface  of  the  cardinal 
area  with  its  tree  margin  concave. 

Brachial  valve  not  observed. 

Remarks.  —  This  species  is  a  close  ally  of  S.  plains  and  might  perhaps  be 
considered  as  only  a  variety  of  that  species.  The  exceedingly  strong, 
bifoliate  dental  lamella'  are  alike  in  both  forms,  but  the  one  here  de- 
scribed is  proportionally  much  broader  and  shorter,  with  the  pedicle 
valve  much  less  strongly  curved  in  an  antero-posterior  direction,  and  with 
a  less  strongly  arched  cardinal  area. 

Horizon . — Burlington  limestone. 

Spiriferella  neglecta  (Hall) 
Plate  LXIV,  Figs.  5-9 ;  Plate  LXV,  Figs.  1-4 

1858.  Spirifcr  mglectus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.'  643,  pi.  20,  fig.  5, 
1875.     Spirifcr  ncglectus  Meek   and   Worthen,    Geol.    Surv.   111.,   vol.    6, 

p.   523.  pi.  30,  figs,   lc,  2a. 
1884.     Spirifera  neglecta  Walcott,  Pal.  Eureka  Dist.,  p.  217,  pi.  18,  fig.  10. 

Description.— Shell  above  medium  size,  usually  wider  than  long,  but 
sometimes  longer  than  wide,  greatest  width  at  about  the  mid-length  of 
the  shell,  the  hinge-line  short,  the  cardinal  extremities  rounded.  The 
dimensions  of  two  individuals,  the  larger  of  which  is  somewhat  distorted, 
are :  length  51  mm.  and  42  mm.,  greatest  width  60  mm.  and  39  mm., 
length  of  hinge-line  28  mm.  and  21  mm.,  thickness  38  mm.  and  28  mm., 
height  of  cardinal  area  11  mm.  and  9  mm. 

Pedicle  valve  strongly  convex  or  gibbous  with  its  greatest  convexity 
posterior  to  the  middle,  sometimes  well  up  towards  the  umbonal  region, 
the  surface  curving  very  abruptly  from  the  umbonal  region  to  the  car- 
dinal margin  and  less  abruptly  to  the  antero-lateral  margins,  the  convex- 
ity of  the  valve  extending  out  to  the  cardinal  extremities ;  the  beak  pointed 
and  incurved ;  cardinal  area  narrow  and  high,  arched,  the  curvature  in- 
creasing towards  the  beak,  the  inferior  portion  sloping  posteriorly  at  an 
angle  of  less  than  110  degrees  to  the  plane  of  the  valve,  divided  by  a  large 
delthyrium  which  occupies  the  central  half  of  the  total  width  of  the 
true  area  on  the  hinge-line,  the  actual  surface  of  the  area  being  limited 
to  two  narrow  bands  which  pass  obliquely  from  the  hinge-line  to  the  beak, 
the  lateral  margins  of  the  area  not  defined,  its  surface  passing  laterally 
without  demarcation  into  a  false  cardinal  area  which  rounds  gradually 
into  the  lateral  slopes  of  the  valve ;  lateral  slopes  of  the  valve  each  bearing 


416  MISSISSIIMMAN   BRACHIOPODA 

from  <i  lo  S  broad,  depressed,  rounded,  more  or  less  obscure,  simple  plica 
tions,  which  become  obsolete  towards  the  cardinal  extremities;  mesial 
sinus  originating  at  the  beak,  becoming  broad  and  moderately  deep 
towards  the  front,  it  is  nearly  flat  in  the  bottom  or  more  often  is  occu- 
pied by  a  broad,  depressed  convex  region  which  can  scarcely  be  called 
a  plication,  although  in  the  narrower  examples  it,  assumes  more  the  form 
of  a  plication,  the  lateral  slopes  of  the  sinus  are  convex  and  pass  without 
demarcation  into  the  surface  of  the  lateral  slopes  of  the  valve. 

Brachial  valve  a  Little  less  convex  than  the  pedicle,  its  greatest  con- 
vexity near  the  middle,  the  convexity  extending  out  to  the  cardinal  ex- 
tremities; the  beak  slightly  incurved  and  extending  a  little  beyond  the 
hinge-line ;  the  mesial  fold  narrow  at  the  beak,  becoming  broad  and  in 
large  examples  very  high  in  front  where  it  is  rounded  and  free  from 
plications;  lateral  slopes  bearing  plications  similar  in  form  and  number 
to  those  of  the  opposite  valve. 

Shell  structure  punctate ;  the  minute  surface  markings  not  preserved, 
but  there  are  concentric  lines  of  growth  which  are  sometimes  strongly 
developed  and  crowded  towards  the  anterior  margin. 

In  the  internal  casts  of  the  shell  preserved  in  residual  cherts,  the 
dental  lamellae  of  the  pedicle  valve  are  seen  to  be  elongate,  extending 
nearly  one-third  the  total  length  of  the  valve  from  the  beak  towards 
the  anterior  margin,  and  diverging  only  to  a  moderate  degree;  the  mus- 
cular impressions  in  the  same  specimens  are  scarcely  defined. 

h'i  marks. — This  species  is  so  distinctly  marked  that  it  cannot  be  con- 
fused with  any  other  form.  In  the  rounding  of  the  lateral  slopes  of  the 
pedicle  valve  into  the  false  cardinal  area  it  resembles  Spirifer  sub- 
car diiformis,  but  it  attains  a  larger  size  than  that  species  and  differs  from 
it  in  the  lack  of  any  line  of  sharp  demarcation  between  the  false  and  the 
true  cardinal  area,  as  well  as  in  the  lack  of  plications  in  the  fold  and 
sinus,  and  in  the  punctate  structure  of  the  shell.  In  general  form  the 
species  most  closely  resembles  S.  plena,  but  the  cardinal  area  of  the 
pedicle  valve  of  that  species  is  much  larger  and  more  defined,  and  the 
plications  of  the  shell  are  narrower  and  much  more  numerous. 

Horizon. — Keokuk  limestone. 

Spiriferella  ?  schucherti  (Rowley) 
Plate  XXXV,  Figs.  59-63 
1900.     Spirifer  schucherti  Rowley,  Am.  Geol.,  vol.  25,  p.  261,  pi.  5,  figs. 
15-17,  59. 

Description.  —  Shell  small,  suborbicular  in  outline,  a  little  wider  than 
long,  the  greatest  width  at  about  the  mid-length  of  the  shell,  the  hinge- 
line  shorter  than  the  greatest  width,  the  cai'dinal  extremities  rounded. 
The  dimensions  of  a  nearly  perfect  specimen,  a  metatype,  are:  length  of 
pedicle  valve  8.9  mm.,  length  of  brachial  valve  7.5  mm.,  greatest  width 


SPIRIFERELLA  417 

9.4  mm.,  thickness  6.2  mm.,  length  of  hinge-line  5  mm.,  width  of  mesial 
sinus  in  front  3.7  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbo  prom- 
inent, the  surface  curving  abruptly  to  the  cardinal  margin,  and  more 
gently  to  the  lateral  and  anterior  margins;  the  mesial  sinus  originating 
at  the  beak,  sharply  defined  throughout  its  entire  length  by  a  pair  of 
strong,  rounded  plications,  rather  shallow,  of  moderate  width  and  round- 
ed  in  the  bottom,  either  without  plications  or  with  a  single,  simple  median 
one  originating  back  of  the  middle  of  the  shell  and  continuing  to  the 
front  margin  with  gradually  increasing  strength,  but  never  becoming  as 
strong  as  those  of  the  lateral  slopes  of  the  valve ;  the  beak  prominent, 
pointed,  rather  strongly  incurved ;  each  lateral  slope  of  the  valve  bearing 
from  four  to  six  rounded,  simple  plications  which  originate  along  the 
cardinal  margin,  the  cardinal  area  small,  concave,  with  the  curvature 
increasing  towards  the  beak,  the  lateral  margins  not  sharply  defined, 
the  surface  curving  without  interruption  into  the  lateral  slopes  of  the 
valve. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  near 
the  middle,  the  surface  curving  more  abruptly  to  the  cardinal  margin 
on  each  side  of  the  beak,  and  gently  to  the  antero-lateral  margins,  a 
little  compressed  towards  the  cardinal  extremities;  mesial  fold  well  de- 
fined from  the  beak  to  the  front  margin,  scarcely  elevated  above  the  gen- 
eral convexity  in  the  posterior  half  of  the  valve,  and  only  moderately 
elevated  towards  the  front,  a  little  flattened  on  top  or  with  a  slight  longi- 
tudinal depression  which  is  much  fainter  than  the  median  plication  in 
the  sinus  of  the  opposite  valve;  beak  small,  incurved,  only  slightly  pro- 
jecting beyond  the  cardinal  margin ;  each  lateral  slope  marked  by  from 
four  to  six  simple,  rounded  plications  entirely  similar  to  those  of  the 
pedicle  valve.  Surface  of  both  valves  marked  by  very  fine,  closely 
crowded  granules  or  papilla1,  and  the  shell  structure  rather  coarsely,  but 
closely,  punctate. 

Remarks. — In  its  general  outline  this  little  .shell  at  once  suggests  a 
minute  individual  of  Spirifer  sub orbicularis  or  S.  chouteauemis,  but  it 
differs  notably  from  either  of  these  species  in  the  presence  of  the  minute 
surface  papillae  and  the  punctate  shell  structure.  The  punctate  structure 
of  the  shell  suggests  the  genus  Spiriferitia,  but  the  general  form  is  totally 
different  from  any  of  our  other  species  of  that  genus,  all  of  which  have 
a  more  or  less  elongate  hinge-line  and  well  defined  cardinal  area  with 
sharply  defined  lateral  margins.  The  internal  features  of  the  shell  have 
not  been  observed  so  that  the  presence  or  absence  of  a  median  septum 
in  the  pedicle  valve  is  not  known,  if  such  a  septum  be  present  the  species 
should  doubtless  be  placed  in  the  genus  Spiriferina,  in  spite  of  its  unusual 
external  form.    On  the  whole  this  little  shell  seems  to  agree  most  closely, 

—14 


418  M  ississiiM'IAN   BRACHIOPODA 

in  all  those  characters  which  can  be  observed,  with  such  punctate  shells 
as  Spiriferella  neglecta.  It  has  the  same  rotund  I'orin  with  short  hinge- 
line  and  ill-defined  cardinal  area,  and  if  it  should  be  shown  that  it  pos- 
sesses greatly  elongate  dental  lamella-  in  the  pedicle  valve,  without  a 
median  septum,  the  reference  to  Spiri/'i  r<  Hit.  as  used  in  this  place,  is  doubt- 
U  s.s  correct. 
Horizon.  -Lower  Burlington  limestone. 

Genus  ACANTHOSPIRA  n.  gen. 

Description. — Shell  small,  spiriferoid  in  form,  and  so  far  as  known 
agreeing  entirely  with  Spirifer  in  its  internal  characters  and  in  its 
larger  external  features.  The  essential  generic  character  consists  in  the 
presence  of  tine  spines  upon  the  surface,  which  in  the  genotype  are  ar- 
ranged in  regularly  radiating  series  along  the  summits  of  the  plications, 
and  in  similar  rows  on  the  fold  and  sinus. 

Remarks. — This  genus  is  established  upon  a  single  species  which  has 
been  referred  to  Spiriferina  by  its  original  author,  but  the  shell  structure 
is  apparently  non-punctate  and  there  is  no  evidence  of  a  median  septum 
in  the  pedicle  valve.  The  presence  of  surface  spines,  such  as  the  species 
possesses,  is  entirely  foreign  to  the  genus  Spirifer,  and  consequently  the 
shell  has  been  made  the  type  of  a  new  genus. 

ACANTHOSPIRA  ACICULIFERA    (Rowley) 

Plate  XXXV,  Figs.  64-72 

1893.     Spirifera  adculifera  Rowley,  Am.  Geol.,  vol.  12,  p.  307,  pi.  14,  figs. 

13-14. 
1908.     Spiriferina  adculifera  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  84,  pi.  18,  figs."  13-15. 

Description. — Shell  small,  broader  than  long,  semicircular  in  outline, 
hinge-line  a  little  shorter  than  the  greatest  width,  the  cardinal  extremities 
a  little  rounded.  The  dimensions  of  the  holotype  are :  length  of  pedicle 
valve  4.1  mm.,  length  of  brachial  valve  3.9  mm.,  greatest  width  5.6  mm., 
thickness  3  mm.,  length  of  hinge-line  4.8  mm.,  height  of  cardinal  area  1.2 
mm.,  width  of  mesial  sinus  in  front  2  mm. 

Pedicle  valve  subpyramidal  in  form,  most  prominent  in  the  umbonal 
region,  the  surface  sloping  from  the  umbo  to  the  lateral  margins  in  nearly 
straight  or  slightly  concave  lines,  the  curvature  to  the  antero-lateral  and 
anterior  margins  gently  convex ;  mesial  sinus  non-plicate,  sharply  defined, 
originating  at  the  beak,  rather  shallow,  flattened  in  the  bottom ;  beak 
small,  moderately  incurved ;  cardinal  area  moderately  high,  nearly  flat 
below,  becoming  concave  towards  the  beak,  the  lower  flattened  portion 
lying  in  nearly  a  right  angle  to  the  plane  of  the  valve,  the  lateral  mar- 
gins not  sharply  defined,  the  surface  curving  into  the  lateral  slopes  of 
the  valve;  an  inner  or  secondary  area  is  present,  bounded  laterally  by  a 


ACANTHOSPUtA  419 

pair  of  slightly  elevated  ridges  which  diverge  from  the  heak  to  the  hinge- 
line  which  they  meet  a  little  less  than  half-way  from  the  margins  of  the 
delthyrium  to  the  cardinal  extremities,  no  differentiation  in  the  ornamen- 
tation of  the  two  portions  of  the  area  is  recognizable  in  the  type  speci- 
men ;  delthyrium  open,  rather  large,  its  width  at  the  base  about  equal  to 
its  height ;  each  lateral  slope  marked  by  about  seven  simple,  rounded, 
radiating  plications  which  originate  along  the  cardinal  margin,  the  pli- 
cations bounding  the  sinus  are  the  largest,  the  others  growing  successively 
smaller  to  the  last  one,  which  is  almost  obsolete. 

Brachial  valve  depressed  convex,  becoming  compressed  towards  the 
cardinal  extremities,  most  convex  posterior  to  the  middle,  gently  convex 
to  the  antero-lateral  and  anterior  margins ;  mesial  fold  non-plicate,  well 
defined,  originating  at  the  beak,  rather  low,  flattened  on  top ;  the  beak 
small,  scarcely  incurved,  only  slightly  protuberant  beyond  the  cardinal 
margin;  each  lateral  slope  marked  by  six  plications  entirely  similar  to 
those  of  the  opposite  valve  and  alternate  with  them. 

Aside  from  the  plications  the  surface  of  each  valve  is  marked  by  regu- 
larly arranged,  minute  tubercles  or  papilla1  which  doubtless  supported 
slender  spines  in  the  living  shell,  a  single  radial  row  of  such  tubercles  is 
present  upon  the  summit  of  each  plication,  in  addition  to  which  a  single 
row  occupies  the  median  line  of  the  sinus  of  the  pedicle  valve,  and  two 
rows  the  flattened  portion  of  the  fold  of  the  brachial  valve ;  very  fine, 
more  or  less  obscure,  concentric  lines  of  growth  are  also  present  upon 
each  valve.     Shell  structure  apparently  not  punctate. 

Remarks. — In  the  apparent  absence  of  any  punctate  shell  structure, 
this  species  does  not  conform  with  the  generic  definition  of  Spiriferina,  the 
genus  to  which  it  has  been  referred  by  its  author.  The  internal  charac- 
ters of  the  pedicle  valve  are  not  clearly  defined  because  of  the  complete 
retention  of  the  shell  substance,  but  the  valve  is  sufficintly  transparent  to 
clearly  show  the  presence  of  a  pair  of  dental  lamella?  diverging  from  the 
beak  in  line  with  the  bounding  plications  of  the  mesial  sinus,  and  extend- 
ing for  about  one-third  the  length  of  the  valve,  while  no  median  septum  is 
apparent  and  is  probably  wanting  in  the  species.  The  absence  of  the 
punctate  shell  structure,  the  dental  lamella?  not  united  to  form  a  spondy- 
lium,  and  the  open  delthyrium  likewise  exclude  the  species  from  Cyrtina. 
Syringothyris  and  its  allies  are  also  excluded  by  reason  of  the  non-punctate 
shell  and  the  absence  of  the  peculiar  surface  markings  of  those  genera, 
and  no  delthyrial  plate  or  syrinx  is  known  to  be  present.  The  species 
agrees  most  closely  with  the  members  of  the  genus  Spirifer,  but  the  pres- 
ence of  the  regularly  arranged,  minute  spines  of  a  character  foreign  to  that 
genus.  The  species  is,  therefore,  considered  as  the  type  of  the  new  genus 
Acanthospira. 

Horizon. — Louisiana  limestone. 


420  MISSISSIP]  IAN    BRACHIOPODA 

Genus  MABTIN1A  McCoy 

Description.-  Shells  usually  of  medium  size  or  smaller,  subcircular, 
subovate  or  subelliptical  in  outline,  the  hinge-line  short,  the  cardinal  ex- 
tremities rounded,  1  ho  surface  of  the  valves  smooth  or  nearly  so.  The 
pedicle  valve  with  a  small  cardinal  area  whose  lateral  margins  are  not 
sharply  defined,  the  surface  curving  with  Little  or  no  differentation  into 
the  lateral  slopes  of  the  valve,  the  delthyrium  rather  large;  internally 
neither  dental  lamella  nor  median  septum  are  present,  the  muscular  scars 
are  small,  scarcely  impressed  and  ill-defined.  In  the  brachial  valve  the 
muscular  scars  are  also  inconspicuous,  the  crura  and  primary  lamella? 
of  the  brachidium  are  elongate,  the  bases  of  the  spiral  coils  are  situated 
well  forward  and  their  apices  are  directed  towards  the  cardinal  ex- 
1  remit  ies. 

Remarks. —  In  general  external  form  and  in  the  smoothness  of  the  shell 
the  members  of  this  genus  resemble  some  of  the  athyroid  genera,  but  they 
always  possess  a  distinct  cardinal  area,  although  it  is  small,  with  a  rather 
large,  open  delthyrium.  YYaagen1  has  pointed  out  the  presence  of  a  min- 
utely punctate  structure  in  the  epidermal  layer  of  the  shells  of  this  genus, 
a  structure  which  does  not  penetrate  the  inner  layers  of  the  shell,  and 
considers  it  as  one  of  the  generic  characters.  This  feature,  however,  has 
not  been  observed  in  any  of  the  American  shells  which  have  come  under 
observation,  a  fact  which  may  be  due  to  the  destruction  of  the  epidermal 
layer  of  the  specimens  observed. 

Mabtinia  contracta  (Meek  and  Worthen) 
Plate  LXXV,  Figs.  1-10 

1861.     Spirifera  glabra  var.  contracta  Meek  and  Worthen,  Proc.  Acad.  Nat. 

Sci.  Phil.,  p.  143. 
1866.     Spirifer  glaber  var.  contractus  Meek  and  Worthen,  Geol.  Surv.  111., 

vol.  2,  p.  298,  pi.  23,  figs.  5a-b. 
1888.     Spirifer  glaber  Herrick,  Bull.  Sci.  Lab.  Denison,  Univ.  vol.  4,  pi.  11. 

fig.  15. 
1891.     Spirifer   (Martinia)   contractus  Whitfield,  Ann.  N.  Y.  Acad.  Sci., 

vol.  5,  p.  583,  pi.  13,  figs.  17-19. 

1894.  Spirifera  contracta  Keye:s,  Mo.  Geol.  Surv.,  vol.  5,  p.  83. 

1895.  Spirifera  (Martinia)  contracta  Whitfield,  Geol.  Surv.  Ohio,  vol.  7, 

p.  471,  pi.  9,  figs.  17-19. 
1909.     Martinia  contracta  Bassler,  Va.  Geol.  Surv.,  Bull.  No.  II  A,  pi.  29, 

fig.  11. 
1911.     Martinia  contracta  Morse,  Proc.  Ohio  State  Acad.  Sci.,  vol.  5,  p.  375, 

figs.  lOa-c. 

Description. — Shell  subovate  or  ovate-subquadrangular  in  outline, 
longer  than  wide  or  with  the  length  and  width  subequal,  hinge-line  short, 

l  Mem.  Geol.  Surv.  India,  ser.  13,  pt.  1,  p.  529.   (1882.) 


MARTINIA  421 

the  cardinal  extremities  rounded,  the  greatest  width  near  the  mid-length 
of  the  shell.  The  dimensions  of  three  nearly  perfect  specimens  are: 
length  of  pedicle  valve  28.3  mm.,  21.5  mm.  and  20.7  mm.,  length  of  brachial 
valve  24  mm.,  18  mm.  and  17.6  mm.,  maximum  width  24.5  mm.,  20.9  mm. 
and  20.9  mm.,  length  of  hinge-line  13  mm.,  12.2  mm.  and  9  mm.,  thickness 
19.8  mm.,  14  mm.  and  14.3  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbo  prominent  and  projecting  posteriorly  beyond  the  hinge- 
line,  the  surface  curving  abruptly  to  the  cardinal  margin,  more  gently  to 
the  lateral  margins  and  most  gently  to  the  anterior  margin ;  mesial  sinus 
originating  in  the  umbonal  region,  shallow  or  of  moderate  depth,  rounded 
in  the  bottom  or  subangular  along  the  median  line,  ill-defined  laterally,  a 
little  produced  anteriorly ;  beak  rather  prominent,  strongly  incurved  ; 
cardinal  area  small,  strongly  arched,  the  lateral  margins  not  sharply  de- 
fined, the  surface  curving  almost  without  interruption  into  the  lateral 
slopes  of  the  valve  except  towards  the  cardinal  extremities ;  delthyrium 
large,  broadly  triangular,  occupying  one-half  or  nearly  one-half  of  the 
hinge-line  at  its  base. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  curving  abruptly  to  the  cardinal  mar- 
gin  and  sloping  with  a  gentle  convexity  from  the  median  line  to  the  lat- 
eral margins,  convex  along  the  median  line  from  the  beak  to  the  front 
with  an  increasing  curvature  posteriorly,  sometimes  a  little  compressed 
towards  the  cardinal  extremities ;  mesial  fold  ill-defined,  scarcely  differ- 
entiated in  the  posterior  half  of  the  valve,  it  is  rounded  on  top  and  often 
has  a  slight  mesial  depression  in  the  anterior  half  of  the  valve  ;  beak  small, 
incurved ;  cardinal  area  very  narrow. 

The  surface  markings  of  both  valves,  as  shown  upon  exfoliated  speci- 
mens, consist  of  fine,  radiating  costa?,  about  2  or  3  of  which  occupy  one 
millimeter  near  the  margin,  becoming  finer  towards  the  beak,  these  costa? 
increase  usually  by  implantation  and  are  of  such  strength  that  they  must 
have  been  present  upon  the  surface  of  non-exfoliated  shells ;  crossing  the 
radiating  costae  are  exceedingly  fine  concentric  lines  whieh  are  usually 
crowded  at  intervals,  especially  in  the  anterior  half  the  shell,  in  stronger 
lines  of  growth. 

Remarks.- — In  the  original  description  of  this  species  the  presence  of 
radiating  markings  is  noted  but  they  are  described  as  being  too  fine  to  be 
observed  with  the  unaided  eye.  Upon  the  specimens  here  described  the 
radiating  costse  are  very  distinct,  agreeing  more  closely  with  the  shells 
from  Ohio  which  Whitfield  has  referred  to  the  species  than  to  the  orig- 
inals of  Meek  and  Worthen.  The  specimens  observed  exhibit  consider- 
able variation  in  their  proportional  length  and  width,  and  in  the  angular- 
ity of  the  mesial  sinus,  the  specimens  with  the  more  angular  sinus  having 


422  MISSISSIPPIAN   BRACHIOPODA 

the  more  conspicuous  mesial  depression  along-  the  median  line  of  the  fold 
of  the  brachial  valve. 

Horizon. — Chester  group,  Okaw  limestone. 

.Mahtinia  sulcata  n.  sp. 
Plate  IA'XV,  Figs.  11-14 

Description.—  Shell  below  medium  size  broadly  suliovate  in  outline, 
wider  than  long,  the  greatest  width  near  the  mid-length,  the  hinge-line 
much  shorter  than  the  greatest  width,  the  cardinal  extremities  rounded. 
The  dimensions  of  a  nearly  complete  specimen  are  :  length  of  pedicle  valve 
21.4  mm.,  length  of  brachial  valve  18.5  mm.,  greatest  width  22.5  mm., 
length  of  hinge-line  9.5  mm.,  thickness  1:5.3  mm. 

Pedicle  valve  strongly  convex,  the  surface  curving  abruptly  to  the  car- 
dinal margin  and  somewhat  more  gently  to  the  lateral  and  anterior  mar- 
gins, not  compressed  towards  the  cardinal  extremities;  the  beak  short  and 
blunt  rather  strongly  incurved;  cardinal  area  small  with  lateral  margins 
not  sharply  defined,  its  surface  curving  into  that  of  the  lateral  slopes  of 
the  valve  without  interruption,  the  delthyrium  about  as  wide  as  high; 
mesial  sinus  obsolete  at  the  beak  and  in  the  umbonal  region,  originating 
posterior  to  the  middle  of  the  valve  and  rapidly  deepening  anteriorly,  be- 
coming very  profound  and  subangular  in  the  bottom  towards  the  front, 
and  moderately  produced  as  an  anterior  extension  of  the  valve,  not 
sharply  defined  laterally;  lateral  slopes  regularly  convex. 

Brachial  valve  usually  a  little  less  convex  than  the  pedicle,  the  greatest 
depth  near  and  anterior  to  the  middle  of  the  valve,  the  surface  curving 
more  abruptly  to  the  cardinal  margin,  gently  convex  to  the  lateral  mar- 
gins, the  median  line  from  the  beak  to  the  front  is  convex  posteriorly, 
becoming  nearly  straight  in  the  central  portion  and  in  full  grown  shells 
continuing  straight  to  the  front  or  more  often  becoming  a  little  concave ; 
the  umbonal  region  not  prominent;  the  beak  small  and  inconspicuous; 
the  mesial  fold  obsolete  in  the  posterior  half  of  the  valve  but  becoming 
rather  strongly  elevated  in  front  where  it  is  broadly  rounded  and  ill- 
defined  laterally. 

The  surface  of  both  valves  marked  by  very  fine  and  inconspicuous  radi- 
ating markings  which  can  usually  be  seen  only  with  difficulty,  also  by  ex- 
ceedingly fine  and  inconspicuous  concentric  lines  of  growth.  Both  these 
sets  of  markings  are  so  faint  that  the  surface  appears  to  be  perfectly 
smooth  except  upon  close  examination. 

Remarks. — This  species  differs  from  M.  contractu  in  its  proportionally 
shorter  and  broader  form,  its  much  more  profound  mesial  sinus  towards 
the  front  of  the  pedicle  valve,  and  in  the  less  conspicuous  radiating  mark- 
ings of  the  shell. 

Horizon. — Chester  group. 


AMBOCCELIA  423 

Genus  AMBOCCELIA  Hall 

Description. — Shells  small,  plano-convex  or  slightly  concavo-convex, 
snbcircular  to  subsemielliptical  in  outline,  the  hinge-line  usually  a  little 
shorter  than  the  greatest  width  of  the  shell,  the  cardinal  extremities 
rounded.  Surface  of  valves  smooth  or  with  fine  concentric  lines  of 
growth,  rarely  minutely  spinose,  shell  substance  not  punctate.  Pedicle 
valve  strongly  convex  with  very  prominent  umbonal  region,  the  beak 
strongly  incurved,  marked  by  a  narrow,  median,  groove-like  sinus  which 
is  usually  strongest  posteriorly;  cardinal  area  well  defined,  concave,  the 
delthyrium  rather  large  and  open,  with  incomplete  deltidial  plates. 
Internally  the  hinge-teeth  are  prominent,  with  recurved  tips,  not  sup- 
ported by  dental  lamella5 ;  the  muscular  area  small,  the  interior  surface 
about  the  muscular  scars  strongly  pitted.  Brachial  valve  convex  at  the 
beak,  becoming  flat  or  concave  anteriorly,  with  a  rather  broad  cardinal 
area  lying  in  nearly  a  right  angle  to  the  area  of  the  opposite  valve ;  car- 
dinal process  bifurcate  posteriorly,  elongate,  resting  on  the  bottom  of 
the  valve  except  at  the  posterior  extremity,  the  spires  of  the  brachidium 
loosely  coiled  with  few  volutions,  attached  by  long  crura  which  are 
continuous  with  the  primary  lamellae,  the  jugum  in  the  same  rudimentary 
condition  as  in  Spirifer. 

Remarks. — This  genus  of  small  shells  may  be  easily  recognized,  in  most 
cases,  from  the  detached  pedicle  valves,  the  condition  in  which  the  species 
most  commonly  occur  in  our  faunas,  by  reason  of  the  smooth  surface,  the 
prominence  of  the  umbonal  region  and  the  narrow,  groove-like  mesial 
sinus.  The  genus  is  represented  by  several  species,  all  of  which  are 
restricted  to  the  Kinderhook  faunas. 

AMBOCCELIA   MINUTA  White 

Plate  LXXV1I,  Figs.  44-54 

1862.     Ambocoelia  (Spirifer?)  minuta  White,  Proc.  Boston  Soc.  Nat.  Hist., 

vol.  9,  p.  26. 
1894.     Ambocoelia  minuta  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  90. 
1908.     Ambocoelia  minuta  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 

2nd  ser.,  p.  85,  pi.  18,  figs.  21-24. 

Description. — Shell  minute,  subplanoconvex,  subsemielliptical  in  out- 
line, the  hinge-line  a  little  shorter  than  the  greatest  width  of  the  shell, 
the  cardinal  extremities  rounded.  The  dimensions  of  an  average  in- 
dividual are:  length  of  pedicle  valve  2.3  mm.,  length  of  brachial  valve 
2  mm.,  greatest  width  2.2  mm.,  length  of  hinge-line  1.5  mm.,  thickness 
1.9  mm.,  the  largest  examples  observed  do  not  exceed  3  mm.  in  maximum 
length. 

Pedicle  valve  gibbous,  the  greatest  depth  opposite  the  hinge-line,  the 
umbo  prominent,  the  surface  curving  abruptly  from  the  umbonal  region 


424  mississii'I'I.W    BRACHIOPODA 

to  the  cardinal  margin  and  a  little  more  gently  to  the  lateral  and  an- 

terior  margins;  beak  obtuse,  scarcely  incurved;  cardinal  area  high,  the 
inferior  portion  nearly  flat,  and  lying  at  an  angle  of  about  90  degrees  to 
the  plane  of  the  valve,  becoming  a  little  arched  towards  the  beak,  the  lat- 
eral margins  not,  defined,  the  surface  curving  with  almost  no  demarcation 
into  the  lateral  slopes  of  the  valve;  llie  delthyrium  large,  open,  a  little 
higher  than  wide;  the  lateral  slopes  convex,  smooth;  mesial  sinus  narrow 
and  shallow,  rounded  in  the  bottom,  not  sharply  defined  laterally,  orig- 
inating in  the  ambonal  region  anterior  to  the  beak,  sometimes  nearly  or 
quite  obsolete. 

Brachial  valve  nearly  flat,  the  beak  obtusely  pointed  and  produced 
horizontally  a  little  beyond  the  binge-line,  the  surface  most  prominent 
in  the  unibonal  region,  a  little  compressed  towards  the  cardinal  ex- 
tremities, the  mesial  portion  of  the  valve  depressed  in  a  broad,  shallow, 
ill-defined  sinus  which  originates  at  about  the  posterior  third  of  the 
valve  and  widens  rapidly  until  it  occupies  nearly  one-half  the  total 
width  of  the  valve  towards  the  front. 

Both  valves  are  entirely  non-plicate,  but  the  surface  is  completely 
covered  with  minute,  imbricating  spines  in  perfectly  preserved  specimens. 

Remarks. — This  species  occurs  in  great  numbers  in  the  shaly  partings 
near  the  base  of  the  Louisiana  limestone,  many  complete  examples  being 
recovered  from  the  washings.  The  species  is  characterized  by  its  minute 
size,  by  the  gibbosity  of  the  pedicle  valve  and  its  obtuse  beak,  and  by 
the  character  of  the  minute  surface  markings. 

Horizon. — Louisiana  limestone  of  the  Kinderhook. 

Amboccelia  parva  Weller 
Plate  LXXVII,  Figs.  32-35 

1899.     Ambococlia  parva  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  9,  p.  20, 
pi.  4,  figs.  1-4. 

Description. — -Shell  small,  subovate  in  outline,  the  length  and  width 
equal  or  the  width  greater  than  the  length,  the  hinge-line  shorter  than 
the  greatest  width  of  the  shell,  the  cardinal  extremities  rounded.  The 
dimensions  of  two  pedicle  valves  are :  length  4.7  mm.  and  3.4  mm.,  width 
4.8  mm.  and  3.6  mm.,  convexity  2.3  mm.  and  1.3  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  umbonal  region  projecting  notably  beyond  the  hinge-line 
posteriorly ;  the  surface  somewhat  flattened  in  the  median  region  from 
the  beak  to  the  anterior  margin,  laterally  the  surface  curves  abruptly 
towards  the  cardinal  extremities  and  a  little  more  gently  to  the  lateral 
margins ;  beak  obtusely  rounded,  moderately  incurved ;  cardinal  area  of 
moderate  height,  arched,  apparently  not  sharply  defined  at  its  lateral 
margins,  the  surface  curving  into  the  lateral  slopes  of  the  valve  without 


AMBOCCELIA  425 

differentiation;  lateral  slopes  convex,  smooth;  mesial  sinus  originating 
at  the  beak,  narrow,  angular  in  the  bottom,  not  sharply  defined  laterally, 
dividing  the  median  flattened  region  of  the  valve  along  its  middle  line. 

Brachial  valve  not  known. 

Remarks. — The  type  specimens  of  this  species  are  from  a  fine-grained 
yellow  sandstone  from  which  all  the  shell  substance  has  been  removed. 
The  specimens,  however,  are  not  internal  casts  of  the  shell  but  apparently 
retain  the  external  configuration  of  the  shell.  The  surface  of  the  shell, 
as  preserved,  is  entirely  smooth  without  lines  of  growth  or  other  surface 
ornamentation.  The  species  differs  from  A.  minuta  in  its  larger  size, 
its  less  gibbous  pedicle  valve  with  the  umbonal  region  projecting  farther 
posteriorly,  and  in  the  absence  of  the  covering  of  fine  surface  spines. 

Horizon. — Xorthview  sandstone  of  the  Kinderhook. 

Amboccelia  unionensis  n.  sp. 
Plate  LXXVII.  Figs.  36-43 

Description. — Shell  small,  wider  than  long,  subelliptical  in  outline,  the 
hinge-line  shorter  than  the  greatest  width,  the  cardinal  extremities 
.rounded.  The  dimensions  of  two  pedicle  valves  are:  length  8.3  mm. 
and  5.4  mm.,  width  10.3  mm.  and  5.6  mm.,  convexity  3.6  mm.  and  2.5 
mm.,  length  of  hinge-line  7.5  mm.  and  3.6  mm. 

Pedicle  valve  strongly  convex,  subhemispherical  in  form,  the  greatest 
convexity  near  or  posterior  to  the  middle,  the  umbonal  region  broad  and 
projecting  posteriorly  beyond  the  hinge-line  to  only  a  moderate  degree; 
the  surface  curving  abruptly  from  the  umbonal  region  towards  the  car- 
dinal margin,  and  more  gently  to  the  lateral  and  anterior  margins;  beak 
short,  obtuse,  only  a  little  incurved ;  cardinal  area  of  moderate  height, 
arched,  the  lateral  margins  slightly  defined,  sloping  in  nearly  straight 
or  slightly  concave  lines  from  the  beak  to  the  cardinal  extremities,  the 
delthyrium  large,  its  base  occupying  one-third  or  more  of  the  total  hinge- 
line  ;  lateral  slopes  of  the  valve  smooth,  convex  towards  the  middle  of 
the  valve,  becoming  somewhat  compressed  towards  the  cardinal  ex- 
tremities in  large  individuals;  mesial  sinus  originating  at  the  beak,  nar- 
row, angular  in  the  bottom,  not  sharply  defined  laterally. 

Brachial  valve  much  less  convex  than  the  pedicle,  the  greatest  depth 
about  half  way  between  the  middle  of  the  valve  and  the  posterior  margin, 
the  surface  compressed  towards  the  cardinal  extremities ;  the  beak  ob- 
tusely pointed  and  extending  a  little  beyond  the  hinge-line  posteriorly; 
the  median  portion  of  the  valve  depressed  in  a  broad,  shallow,  ill- 
defined  sinus  which  originates  near  the  beak  and  becomes  rapidly  broader 
towards  the  front. 

The  surface  of  both  valves  marked  by  usually  well  defined  but  not 
always  strong  concentric  lines  of  growth,  aside  from  which  the  surface 
is  apparently  unornamented. 


426  MlSSISSIl'I'IAN   BRACHIOPODA 

Remarks. — This  species  differs  from  A.  minuta  in  its  larger  size,  its 
proportionally  much  less  convex  pedicle  valve,  and  in  the  absence  of 
the  minutely  spinose  surface  markings.  It  is  more  nearly  like  .1.  parva, 
bul  differs  from  that  species  in  its  larger  size,  in  the  more  obtuse  beak 
of  the  pedicle  valve,  and  in  the  more  conspicuous  development  of  the 
concentric  lines  of  growth. 

Horizon. — Kinderhook  (Rockford  limestone). 

A.MBOCCELIA  LEVH3UL.A   Kouley 

Plate  I  AW  VII,  Figs.  26-31 

]!)()().    Ambocoelia  levicula  Rowley,  Am.  Geol.,  vol.  25,  p.  262,  pi.  5,  figs. 

12-14. 
1911.     AmbocozUa  h  vicula  f  Girty,  Bull.  U.  S.  Geol.  Survey,  No.  439,  p.  73, 
pi.  8,  figs.  7-9. 

Description.  —  Shell  small,  broader  than  long,  the  greatest  width  near 
the  mid-length  of  the  shell,  the  hinge-line  much  shorter  than  the  greatest 
width,  the  cardinal  extremities  rounded.  The  dimensions  of  a  very 
perfect  example,  a  metatype,  are:  length  of  pedicle  valve  5  mm.,  length 
of  brachial  valve  4.1  mm.,  greatest  width  5.6  mm.,  thickness  3.4  mm., 
length  of  hinge-line  3.5  mm. 

Pedicle  valve  strongly  convex,  most  prominent  in  the  umbonal  region, 
the  surface  curving  abruptly  to  the  cardinal  margin  on  either  side  of 
the  beak,  and  more  gently  to  the  lateral  and  anterior  margins;  the 
mesial  sinus  faint,  very  narrow  and  shallow,  originating  at  or  near  the 
beak,  becoming  less  well  denned  anteriorly ;  the  beak  prominent  and 
strongly  incurved;  cardinal  area  small,  concave  with  the  curvature  in- 
creasing towards  the  beak,  differentiated  from  the  lateral  slopes  of  the 
valve  along  its  lateral  margins  by  a  slight  angulation  of  the  surface 
extending  from  either  side  of  the  beak  to  the  cardinal  extremities,  the 
delthyrium  rather  large,  its  base  occupying  nearly  one-third  of  the  entire 
hinge-line. 

Brachial  valve  depressed  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  somewhat  compressed  towards  the  cardinal  ex- 
tremities, gently  convex  to  the  antero-lateral  and  anterior  margins ;  a 
mesial  flattening  of  the  valve  originates  in  the  umbonal  region  which 
passes  into  a  rapidly  widening,  but  very  shallow,  ill-defined  mesial  sinus 
anteriorly;  the  beak  very  small,  scarcely  or  not  at  all  incurved,  project- 
ing very  slightly  beyond  the  cardinal  margin. 

Surface  of  both  valves  essentially  smooth  in  the  specimens  examined, 
with  neither  concentric  nor  radiating  markings. 

Remarks.— This  species  is  most  closely  allied  to  A.  parva  from  the  North- 
view  sandstone,  but  differs  from  that  species  in  being  proportionally 
wider,  and  in  having  a  much  fainter  mesial  sinus  in  the  pedicle  valve. 

Horizon. — Burlington  white  chert. 


RETICUIiABIA  427 

Genus  BETICULABIA  McCoy 

Description. — Shells  small,  of  medium  size  or  larger,  subovate,  subcir- 
cular  or  subelliptical  in  outline,  the  hinge-line  shorter  than  the  greatest 
width  of  the  shell,  the  cardinal  extremities  rounded,  the  fold  and  sinus 
moderately  developed  or  essentially  obsolete.  The  pedicle  valve  with  a 
rather  small,  arched  cardinal  area  whose  margins  are  usually  ill-defined, 
the  surface  usually  rounding  with  but  little  or  no  interruption  into  the 
lateral  slopes  of  the  valve ;  the  delthyrium  rather  large  and  open.  Inter- 
nally the  dental  lamella?  are  strong  and  elongate  sometimes  extending  an- 
teriorly along  the  floor  of  the  valve  for  more  than  one-third  its  length, 
they  may  be  nearly  parallel  or  moderately  divergent,  between  them,  in  the 
median  line  of  the  valve,  is  a  strong  median  septum  which  commonly 
reaches  further  anteriorly  than  the  dental  lamella?,  the  muscular  area  sub- 
rhomboidal  in  outline,  usually  not  deeply  impressed.  The  brachial  valve 
less  convex  than  the  pedicle,  with  narrow  cardinal  area ;  internally  the 
brachidium  is  simjilar  to  that  of  Spirifer,  so  far  as  known,  the  muscular 
area  is  elongate  ovate  in  outline  and  faintly  impressed,  often  scarcely 
recognizable,  it  is  divided  longitudinally  by  a  median  septum  of  greater 
or  less  strength,  which  is  sometimes  almost  obsolete.  The  surface  of  both 
valves  is  covered  by  regular,  concentric  rows  of  fine  spines,  which  are  in 
the  form  of  double  tubes,  the  position  of  these  double  tubed  spines  is 
clearly  shown  upon  the  exfoliated  shell  layers  and  sometimes  upon  the 
casts  of  the  interior  of  the  shells,  but  the  tubes  do  not  penetrate  the  full 
thickness  of  the  shell. 

Remarks. — These  shells  have  often  been  considered  as  being  not  gener- 
ically  distinct  from  Spirifer,  but  their  surface  markings  are  so  very  differ- 
ent from  members  of  that  genus  that  most  writers  of  recent  years  have 
given  the  group  full  generic  rank.  The  genus  has  sometimes  been  made 
to  include  a  group  of  species  from  the  Pennsylvanian  and  Permian  faunas 
which  possess  similar  surface  markings  of  concentric  rows  of  double  tubed 
spines,  but  which  differ  from  these  Mississippian  shells  in  the  entire  ab- 
sence of  septal  lamella?  in  either  valve.  It  has  been  pointed  out  by  Girty,1 
however,  that  the  genotype  of  Reticularia  was  one  of  these  septate  shells, 
and  the  non-septate  form  has  been  referred  by  the  same  author  to  the 
genus  Squamnhiria  Gemmellaro.  All  the  Mississippian  species  which  have 
been  observed  possess  the  internal  septal  plates  and  must  be  referred  to 
Reticularia. 

l  Carb.  Form,  and  Faunas  of  Colorado,  p.  387.     (1903.) 


428  MISSISS1PPIAN  BRACHIOPODA 

Reticularia  cooperensis  (Swallow) 
Plate  LXXV,  Figs.  21-33 

1860.    Spirifer  Cooperensis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1, 

p.  643. 
1862.    Spirifer  hirtus  White  and  Whitfield,  Proc.  Boston  Soc.  Nat.  Hist., 

v«.l.  8,  p.  293. 
1865.     Spirit  ra  hirtat  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  119. 

1869.  Spirifera  hirtat  Winchell.  Safford's  Geol.  Tenn.,  p.  442. 

1870.  Spirifera  hirtat  Winchell,  Proc  Am.  Phil.  Soc,  vol.  11,  p.  251. 
isss.     Spirifir  :'  hirtust  Berrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3, 

p.  47,  pi.  3,  fig.  2. 
1888.     Spirifer  hirtus  Merrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  4,  pi.  10, 
fig.  20. 

1894.  Spirifi  ra  cooperensis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  78. 

1895.  Spirifer  hirtus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  38, 

fig.  14. 
1895.    Spirifer  (e.f.)  hirtus  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi. 
84,  figs.  36-37. 

1899.  /.'<  ticularia  coopi  n  nsis  Girty,  Mon.  U.  S.  Geol.  Surv.,  vol.  32,  p.  555, 

pi.  70,  figs.  9a-c. 

1900.  "Reticularia  cooperensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10, 

p.  80,  pi.  2,  fig.  11. 
J901.     Reticularia  cooperensis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 
p.  166,  pi.  14,  figs.  14-15. 

Description. — Shell  below  medium  size,  broader  than  long,  subellipiti- 
cal  in  outline,  the  hinge-line  much  shorter  than  the  greatest  width,  the 
cardinal  extremities  rounded,  the  lateral  margins  regularly  rounded,  the 
anterior  margin  gently  rounded,  sometimes  nearly  straight  in  the  middle. 
The  dimensions  of  a  nearly  perfect  individual  are :  length  of  pedicle  valve 
17.3  mm.,  length  of  brachial  valve  15  mm.,  maximum  width  21.3  mm., 
length  of  hinge-line  12  mm.,  thickness  11.9  mm.,  height  of  cardinal  area 
21.1  mm. 

Pedicle  valve  rather  strongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  curving  abruptly  from  the  umbonal  region  to 
the  cardinal  margin,  much  less  abruptly  to  the  lateral  margins  and  more 
gently  to  the  anterior  margin ;  mesial  sinus  originating  in  the  umbonal 
region,  shallow,  ill-defined,  and  rounded  in  the  bottom,  sometimes  almost 
or  quite  obsolete ;  beak  rather  small,  incurved ;  cardinal  area  of  moderate 
height,  concave  with  the  curvature  increasing  towards  the  beak,  the  lat- 
eral margins  defined  by  only  a  slight  angulation  of  the  surface  from  the 
lateral  slopes  of  the  valve ;  delthyrium  open,  broadly  triangular,  its  width 
at  the  base  being  about  one-half  the  total  width  of  the  cardinal  area.  In- 
ternally the  hinge-teeth  are  strengthened  by  a  pair  of  dental  lamella1 
which  diverge  from  the  beak  in  an  angle  of  20  to  25  degrees  or  sometimes 
considerably  more  and  extend  along  the  floor  of  the  valve  for  about  one- 
fourth  its  length ;  between  the  dental  lamellae  a  median  septum  extends 


RETICULARIA  429 

from  the  beak  to  about  the  middle  of  the  valve,  being  about  twice  the 
length  of  the  dental  lamellae ;  the  muscular  scars  are  obscure,  being 
scarcely  differentiated  from  the  general  inner  surface  of  the  valve ;  the 
shell  itself  is  thin  so  that  the  concentric  markings  of  the  external  surface 
are  clearly  shown  upon  the  internal  casts,  which  are  also  marked  by  fine, 
irregular,  more  or  less  inconspicuous  radiating  costse. 

Brachial  valve  less  strongly  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  surface  curving  somewhat  abruptly  to 
the  cardinal  margin  and  rather  gently  to  the  lateral  and  anterior  mar- 
gins, moderately  compressed  towards  the  cardinal  extremities;  mesial 
fold  obscure  or  obsolete,  when  present  it  is  very  low,  rounded  on  top,  and 
is  ill-defined  laterally;  the  beak  is  small,  short,  and  a  little  incurved,  the 
umbonal  region  projects  a  little  beyond  the  cardinal  margin;  cardinal 
area  narrow,  nearly  horizontal  in  position.  Internally  the  cardinal  pro- 
cess is  scarcely  differentiated  ;  a  median  septum  which  rapidly  becomes 
only  a  slight,  raised  rib  along  the  floor  of  the  valve,  extends  to  a  point 
between  one-third  and  one-half  the  length  of  the  valve  from  the  beak  ; 
at  the  beak  the  cardinal  process  is  flanked  by  a  pair  of  rather  strong  but 
short  crural  plates  which  join  the  median  septum ;  the  muscular  scars  are 
scarcely  or  not  at  all  differentiated  from  the  general  inner  surface  of  the 
valve. 

The  surface  of  both  valves  is  marked  by  moderately  broad,  concentric 
bands  which  are  beset  with  closely  arranged  fimbriae  or  fine  spines,  those 
of  successive  bands  being  imbricating  in  arrangement. 

Remarks.— This  species  is  a  close  ally  of  R.  pseudolineata,  but  is  always 
smaller  and  is  commonly  proportionally  thicker  and  narrower.  Inter- 
nally the  radiating  costal  of  the  shell  which  are  so  characteristic  in 
R.  pseudolineata  are  much  less  strongly  developed  than  in  that  species. 
In  the  condition  of  preservation  in  which  it  is  commonly  found,  the  sur- 
face of  the  shell  is  exfoliated  and  the  exact  nature  of  the  concentric  rows 
of  spines  is  not  clearly  shown,  but  they  are  probably  of  the  double-tubed 
type  similar  to  those  of  R.  pseudolineata. 

The  species  differs  from  R.  temiispinata  of  the  Ohio  Waverly,  in  its 
greater  proportional  length  and  in  the  less  conspicuous  development  of  the 
internal  radiating  costse,  that  species  being  more  nearly  like  a  diminutive 
R.  pseudolineata. 

Ho  rizon . — Kinderhook. 

Reticularia  pseudolineata  (Hall) 
Plate  LXXIV,  Figs.  1-11 ;  Plate  LXXV,  Fig.  20 

1858.     Spirifer  pseudvlineatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  645,  pi.  20, 

fig.  4. 
1883.     Spirifera  pseudolineata  Hall,  Rep.  N.  Y.  State  Geol.  for  1882,  pi. 

(36)    61,   figs.   28-30. 


430  MISSISSII'IMAN   BRACHIOPODA 

1891.     Spirifer  psevdolineatusf  Berrick,  Bull.  Geol.  Soc.  Am.,  vol.  2,  p.  45, 

pi.  1,  fig.  is. 
1894.     Spirifer  pseudolineatus  Ball  and  Clarke,  Int.  to  Study  of  Brach., 

pt.  2,  pi.  25,  fig.  15. 

1894.  Spirifera  pseudolineata  Keyes,  Mo.  Geol.  Siirv.,  vol.  5,  p.  82. 

1895.  Spirifer  pseudolineatus  Hall  and  Clarke.  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  36,  figs.  28-30. 

Description.  Shell  above  medium  size,  transversely  subelliptical  in 
outline  with  the  Lateral  margins  symmetrically  rounded,  length  of  the 
hinge-line  about  two-thirds  the  width  of  Hie  shell,  the  cardinal  extremities 
rounded.  The  dimensions  of  two  nearly  complete  specimens  are:  length 
of  pedicle  valve  32.fi  mm.  and  29.3  mm.,  length  of  brachial  valve  28.2  mm. 
and  24.7  mm.,  maximum  width  38.5  mm.  and  33.3  mm.,  length  of  hinge- 
line  26  mm.  and  22  mm.,  thickness  23  mm.  and  21.4  man.,  height  of  car- 
dinal area  6.5  mm.  and  fi  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  margin,  much  less  abruptly  to  the  lateral  margins  and  still  more 
gently  to  the  anterior  margin;  mesial  sinus  ill-defined,  usually  shallow 
and  of  moderate  width,  obsolete  at  the  beak  but  originating  in  the 
umbonal  region ;  beak  rather  small,  pointed,  incurved,  projecting  beyond 
that  of  the  opposite  valve;  cardinal  area  of  moderate  height,  concave, 
becoming  more  curved  towards  the  beak,  its  lateral  margins  ill-defined, 
the  surface  curving  into  that  of  the  lateral  slopes  of  the  valve  with  only 
slight  differentiation,  the  surface  vertically  striate;  delthyrium  broadly 
triangular,  open.  Internally  the  hinge-teeth  are  supported  by  a  pair 
of  strong  dental  lamella?  which  extend  about  one-fourth  the  length  of 
the  valve  from  the  beak  towards  the  anterior  margin,  diverging  at  an 
angle  between  30  and  40  degrees ;  between  the  dental  lamellae  is  a  long 
median  septum  which  reaches  to  the  middle  of  the  valve  or  farther,  being 
from  two  to  three  times  the  length  of  the  dental  lamella?;  the  muscular 
scars  are  longitudinally  subrhomboidal  or  angularly  subovate  in  outline, 
with  their  surface  usually  nearly  flush  with  the  floor  of  the  valve,  their 
anterior  limit  is  marked  by  a  slightly  raised  ridge  passing  from  the 
posterior  termination  of  the  dental  lamella?  to  the  posterior  extremity 
of  the  median  septum,  the  anterior  portion  of  the  ridge  being  gently 
convex  and  the  posterior  half  usually  nearly  straight ;  the  entire  inner 
surface  of  the  valve,  even  that  of  the  cardinal  area  and  the  greater  part 
of  the  muscular  scar,  is  covered  by  fine  radiating  costa?,  from  2  to  5 
of  which  occupy  the  space  of  1  mm. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
near  or  posterior  to  the  middle,  the  surface  curving  abruptly  from  the 
umbonal  region  to  the  cardinal  margin  and  more  gently  to  the  lateral  and 
anterior  margins,  sometimes  very  slightly  compressed  towards  the  car- 


RETICULARIA  431 

dinal  extremities;  mesial  fold  usually  obscure  or  obsolete  except  near  the 
front  margin  where  it  is  low  and  ill-defined,  but  sometimes  more  prom- 
inent and  originating  in  the  umbonal  region;  the  beak  short,  incurved, 
the  umbonal  region  projecting  beyond  the  cardinal  margin ;  cardinal 
area  narrow,  lying  nearly  in  the  plane  of  the  valve.  Internally  the 
cardinal  process  is  scarcely  more  than  a  small,  concave,  differentiated 
region  of  the  inner  surface  of  the  valve  just  under  the  beak,  marked  by 
fine  vertical  ribs  and  furrows,  anteriorly  from  the  cardinal  process  a 
median  septum  of  greater  or  less  strength  extends  one-third  or  more  of 
the  length  of  the  valve,  and  on  either  side  the  cardinal  process  is  flanked 
by  strong  crural  plates  which  are  joined  to  the  median  septum ;  the 
muscular  scars  are  poorly  defined ;  the  entire  internal  surface  covered  by 
fine  radiating  costaj  similar  to  those  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  concentric  bands  of  crowded,  regu- 
larly arranged,  double-tubed,  oblique  spines,  the  successive  rows  of 
which  are  imbricating  in  arrangement,  the  bases  of  the  spines  are  con- 
tinued posteriorly  to  the  next  concentric  band  as  a  slightly  raised  ridge, 
giving  to  the  surface  of  the  shell  when  slightly  worn  the  appearance  of 
having  both  concentric  and  radiating  markings,  with  the  radiating 
markings  much  finer  than  the  concentric  ones.  The  radiating  costaj 
of  the  interior  of  the  valve  are  not  infrequently  clearly  visible  upon 
partially  exfoliated  specimens. 

Remarks. — Hall's  original  specimen  of  this  species  is  recorded  from 
the  Keokidv  limestone  of  Keokuk,  Iowa.  It  differs  from  most  of  the 
examples  from  that  locality  in  having  a  more  strongly  developed  mesial 
fold  and  sinus,  although  occasional  specimens  are  found  which  have 
this  character  even  more  strongly  marked  than  in  the  type.  The  type 
specimen  is  not  in  a  condition  to  show  the  internal  radiating  costas  of  the 
species  but  this  character  is  well  developed  in  all  specimens  preserved 
in  such  a  condition  as  to  exhibit  it,  and  in  internal  casts  from  the  chert 
it  is  especially  well  shown.  The  species  differs  from  B.  setigera  from  the 
higher  Mississippian  beds,  in  the  strong  development  of  these  internal 
radiating  cost*,  in  the  lesser  development  of  the  fold  and  sinus 
and  in  the  finer  rows  of  concentric  spines.  The  strong  development  of 
the  internal  markings  seems  to  be,  perhaps,  the  most  characteristic 
feature  of  the  species. 

Horizon. — Keokuk  limestone. 

Reticularia  setigera  (Hall) 
Plate  LXXIV,  Pigs.  12-22 

1858.     Spirifer  sctigerus  Hall,  Geol.    Iowa,    vol.  1,  pt.  2.  p.  705,  pi.  27, 

figs.  4a-b. 
1877.     Spirifera  setigera  Hall  and  Whitfield,  U.  S.  Geol.  Expl.  40th  Par., 

vol.  4,  p.  270,  pi.  5,  figs.  17-18. 


4:42  Mississii'HAX    BRACHIOPODA 

L883.     Spirifera  setigera  Hall,  Elep.  N.  V.  State  Geol.  Eor  1882,  pi.  (36) 

61,  figs.  26-27. 
1894.     Spirifer  setigerus  Hall  and  Clarke,  Pal  N.  Y.,  vol.  8,  pt.  2,  pi.  36. 

figs.  2(>-27. 
L894.     Spirifera  s<  tigt  ra  Keyes,  M<>.  Geol.  Surv.,  vol.  5,  p.  83. 
l!K)(i.     It'clicuhiria  si  tigi  rus  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1318, 

pi.  21,  figs.  1-la. 
1906.     Beticularia  pseudolineata  !  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind., 

p.  1317,  pi.  20.  figs.  6-6a;  pi.  21,  fig.  5. 
1911,     Reticularia  setigera  Girty,  Bull.  I'.  S.  Geol.  Survey,  No.  439,  p.  69, 

pi.  S,  fig.  <;. 
Description. — Shell  of  medium  size  or  larger,  usually  a  little  wider 
than  long,  sometimes  with  the  length  and  breadth  nearly  equal,  sub- 
elliptical  or  subcircular  in  outline,  the  hinge-line  about  one-half  the  width 
of  the  shell,  the  cardinal  extremities  rounded.  The  dimensions  of  a  nearly 
perfect  specimen  are:  length  of  pedicle  valve  24  mm.,  length  of  brachial 
valve  21.3  mm.,  maximum  width  27..")  mm.,  length  of  hinge-line  14  mm., 
thickness  17.5  mm.,  height  of  cardinal  area  4.4  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  abruptly  from  the  umbo  to  the  cardinal 
margin,  and  more  gently  to  the  lateral  and  anterior  margins;  mesial  sinus 
originating  at  the  beak  or  in  the  umbonal  region,  shallow  or  of  moderate 
depth,  ill-defined  laterally,  rounded  in  the  bottom;  beak  pointed,  rather 
strongly  incurved ;  cardinal  area  of  moderate  height,  concave  with  in- 
creasing curvature  towards  the  beak,  not  sharply  defined  at  the  lateral 
margins,  the  surface  curving  into  that  of  the  lateral  slopes  with  only  a 
slight  line  of  differentiation,  the  surface  of  the  area  vertically  striate, 
the  lateral  margins  of  the  delthyrium  bordered  by  thin,  elevated,  and 
somewhat  deflected  ridges;  delthyrium  broadly  triangular,  rather  large, 
open.  Internally  the  hinge-teeth  are  supported  by  rather  strong  dental 
lamella3  which  usually  diverge  anteriorly  from  the  beak  at  an  angle  of 
from  25  to  40  degrees,  and  extend  from  one-fourth  to  one-half  of  the  total 
length  of  the  valve ;  between  the  dental  lamella?  is  a  well-developed 
median  septum  which  is  considerably  longer  than  the  lamella?,  sometimes 
reaching  to  the  middle  of  the  valve;  the  muscular  sears  are  rather 
narrow,  limited  laterally  by  the  dental  lamella?,  not  deeply  impressed, 
their  anterior  margins  marked  by  rather  indefinite  raised  ridges  which 
extend  obliquely  from  the  anterior  extremities  of  the  dental  lamella*  to 
the  extremity  of  the  median  septum;  in  the  umbonal  region,  including 
the  surface  of  the  muscular  scars,  the  inner  surface  of  the  valve  is  marked 
by  radiating  costa?  which  rarely  reach  beyond  the  middle  of  the  valve. 

Brachial  valve  less  convex  than  the  pedicle,  the  surface  curving 
abruptly  to  the  cardinal  margin  from  the  umbonal  region,  and  more 
gently  to  the  lateral  and  anterior  margins,  sometimes  a  little  compressed 
towards  the  cardinal  extremities;   mesial   fold  originating  at  the  beak 


RETICULARIA  433 

or  in  the  umbonal  region,  ill-defined  laterally,  rounded  on  top,  low  or  of 
moderate  height;  beak  short  and  incurved,  the  umbonal  region  extending 
a  little  beyond  the  hinge-line;  cardinal  area  small,  lying  in  nearly  the 
plane  of  the  valve,  vertically  marked  by  stria'  similar  to  those  of  the 
opposite  valve.  Internally  the  anterior  face  of  the  cardinal  process  is 
flattened  or  concave,  and  is  marked  by  fine  vertical  grooves,  being 
scarcely  differentiated,  except  by  these  markings,  from  the  surface  of  the 
strong  crural  plates  which  flank  it  on  either  side  anteriorly  from  the 
cardinal  process  a  well-defined  median  septum  extends  for  one-third,  or 
nearly  one-third,  the  length  of  the  valve ;  the  muscular  scars  not  well 
defined;  the  deeper  portion  of  the  valve  marked  by  radiating  costaj 
similar  to  those  in  the  opposite  valve. 

The  surface  markings  of  both  valves  consist  of  regular,  concentric, 
imbricating  rows  of  fine,  double-tubed  spines,  the  bases  of  these  spines 
are  continued  posteriorly  upon  the  surface  of  the  shell  as  slight  ridges 
which  reach  to  the  next  adjacent  concentric  band.  When  partially 
worn,  the  markings  frequently  appear  to  consist  of  rather  regular,  con- 
centric bands,  crossed  by  much  finer  radiating  costre. 

Remarks.  —  This  species  is  a  close  ally  of  B.  pseudclineata,  but  may  be 
distinguished  from  it  by  its  proportionally  narrower  form,  its  more 
strongly  developed  mesial  fold  and  sinus,  the  less  strongly  developed 
internal  radiating  costa?,  and  the  somewhat  more  remote  concentric  rows 
of  rather  coarser  spines  upon  the  external  surface.  In  the  typical  ex- 
pression of  each  species  they  are  not  easily  confused,  but  an  occasional 
example  of  R.  pseudolineata  with  more  strongly  marked  fold  and  sinus 
resembles  this  species,  but  such  specimens  are  commonly  proportionally 
wider. 

The  species  is  typically  developed  in  the  Chester  faunas,  but  it  occurs 
not  uncommonly  in  beds  as  low  as  the  Salem  limestone,  but  these  earlier 
representatives  are  often  of  larger  size.  The  dimensions  which  have  been 
given  are  those  of  a  Chester  specimen  of  about  average  size,  but  in  the 
Salem  limestone  the  species  sometimes  attains  a  length  of  30  or  40  mm., 
being  as  large  as  E.  pseudolineata. 

Horizon.  —  Salem  limestone,  Chester  group. 

Reticularia  salemensis  n.  sp. 

Plate  LXXV,  Pigs.  15-19 

Description. —Shell  above  medium  size,  subelliptical  in  outline,  broader 
than  long,  the  greatest  width  near  the  mid-length  of  the  shell,  the  hinge- 
line  much  shorter  than  the  greatest  width,  the  cardinal  extremities 
rounded.     The  dimensions  of  the  type  specimen  are :    length    of   pedicle 


4I5-J-  MISSISSUT1AN    BKACHIOPODA 

valve  33  nun..  Length  of  brachial  valve  27.5  mm.,  maximum  width  37  mm., 
length  of  hinge-line  22  mm.,  thickness  22.5  mm.,  height  of  cardinal  area 
4.5  mm. 

Pedicle  valve  rather  Btrongly  convex,  the  greatest  convexity  posterior 
to  the  middle,  the  surface  curving  abruptly  from  the  umliuiial  region  to 
the  cardinal  margin,  less  abruptly  to  the  lateral  ami  still  more  gently  to 
the  anterior  margin;  mesial  sinus  shallow,  rather  broad,  ill-defined,  orig- 
inating in  the  umbonal  region;  beak  apparently  of  moderate  size,  in- 
curved; cardinal  area  of  moderate  height,  concave,  the  lateral  margins 
not  defined,  the  surface  curving  into  the  lateral  slopes  of  the  valve  with 
no  line  of  differentiation;  the  delthyrium  open,  broadly  triangular.  Inter- 
nally the  hinge-teeth  are  supported  by  a  pair  of  rather  strong  dental 
lamella'  of  unknown  anterior  extension,  between  which  is  a  median  septum 
whose  anterior  extension  is  also  unknown;  character  of  the  muscular 
sens  and  the  internal  configuration  of  the  valve  unknown. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  pos- 
terior to  the  middle,  the  umbo  projecting  somewhat  beyond  the  cardinal 
line,  the  surface  curving  abruptly  to  the  cardinal  margin  and  much  more 
gently  to  the  lateral  and  anterior  margins,  somewhat  compressed  towards 
the  cardinal  extremities;  mesial  fold  almost  obsolete,  only  slightly  distin- 
guishable towards  the  front  of  the  valve,  where  it  is  only  slightly  differ- 
entiated from  the  general  convexity;  beak  short  and  incurved;  cardinal 
area  inconspicuous.     The  internal  characters  of  the  valve  not  observed. 

Surface  of  both  valves  marked  by  regular  concentric  bands  from  2  to  3 
mm.  in  width  along  the  median  line  of  the  shell,  the  surface  of  each  suc- 
cessive band  being  slightly  but  abruptly  depressed  below  the  one  imme- 
diately preceding  it;  the  concentric  bands  are  marked  by  low,  elongate 
nodes  about  1  mm.  apart,  which  are  arranged  in  more  or  less  regular  radi- 
ating lines  from  the  beak  to  the  lateral  and  front  margins  and  Avhich  are 
more  prominent  towards  the  anterior  margin  of  the  concentric  bands. 
Upon  some  portions  of  the  shell  the  anterior  extremities  of  the  nodes  are 
distinctly  bilobed,  showing  that  they  were  produced  in  double-tubed 
spines. 

Remarks. — The  type  specimen  of  this  species  is  a  nearly  complete  ex- 
ample with  the  beak  of  the  pedicle  valve  slightly  restored.  The  shell 
surface  is  exfoliated  so  that  the  surface  spines  have  nowhere  been  pre- 
served, but  the  character  of  the  nodes  which  represent  the  spine  bases 
are  such  as  to  indicate  that  the  characteristic  double-tubed  spines  of  the 
genus  were  present.  The  species  differs  from  R.  setigera,  which  occurs  in 
the  same  fauna,  in  the  slightly  developed  or  nearly  obsolete  fold  and  sinus 
and  in  the  much  coarser  surface  spines.  From  R.  pseudolineata  of  the  lower 
beds  it  differs  in  the  much  coarser  spines,  somewhat  greater  proportional 
length,  and  apparently  in  the  absence  of  the  distinct  internal  radiating 
costs.     The  internal  characters  of  the  shell  are  not  clearlv  exhibited  in 


PTYCHOSPIRA  435 

the  type  specimen,  although  where  the  beak  of  the  pedicle  valve  is  frac- 
tured the  character  of  the  dental  lamellae  and  median  septum  can  be 
observed. 

Horizon.—  Salem  limestone. 

Family  RHYNCHOSPIRID.E 
Genus  PTYCHOSPIRA  Hall 

Description. — Shells  small,  biconvex,  subcircular  in  outline,  the  hinge- 
line  short,  the  valves  bearing  a  few,  strong,  subangular.  simple  plications. 
Pedicle  valve  with  an  erect  or  moderately  incurved  beak  perforated  by  a 
circular  foramen,  the  cardinal  area  small  and  sharply  defined  along  its 
lateral  margins,  the  delthyrium  more  or  less  completely  closed  by  the 
pseudodeltidium,  not  including  the  foramen.  The  brachial  valve  with 
convexity  about  equal  to  that  of  the  pedicle,  internally  the  hinge-plate  is 
supported  by  a  well-defined  median  septum,  and  the  spires  are  constituted 
of  but  four  or  five  volutions.  The  epidermal  layer  of  the  shell  is  finely 
pitted  but  the  punetations  do  not  continue  into  the  deeper  layers  of  the 
shell. 

E(  marks. — This  genus  is  easily  recognized  by  reason  of  its  subequally 
convex  valves,  its  subcircular  outline,  and  its  few  but  strong  plications. 
Tt  has  only  been  observed  in  faunas  of  Kinderhook  or  lower  Burlington 
age. 

Ptychospira  sexplicata  (White  and  Whitfield) 
Plate  LXXVI,  Figs.  35-46 

3862.     Retzia  sexplicata  White  and  Whitfield.  Proc.  Boston  Soc.  Nat.  Hist., 

vol.  8,  p.  294. 
1892.     Retzia  plicata  Miller,  Adv.  Sheets  18th  Rep.  Geol.  Surv.  Ind.,  p.  62, 

pi.  9.  figs.  29-31. 
1894.     Retzia  plicata  Miller,  18th  Rep.  Geol.  Surv.  Ind.,  p.  316,  pi.  9,  figs. 

29-31. 

1894.  Ptijchospira  sexplicata  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt. 

2,  pi.  36,  figs.  22-23. 

1895.  Ptychospira  (cf.)  sexplicata  Hall  &  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  50,  figs.  13-14. 
1895.     Ptychospira  sexplicata  Hall  and  Clarke,  Pal.  X.  Y.,  vol.  8,  pt.  2, 

pi.  83,  fig.  28. 
1900.     Retzia   ?  raricosta  Rowley,  Am.  Geol.,  vol.  25.  p.  266,  pi.  5,  figs. 

34-37. 
1904.     Ptijchospira  sexplicata  Greger,  Am.  Geol.,  vol.  33,  p.  15. 
1909.     Ptychospira  sexplicata  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  pi.  315, 

pi.  14,  fig.  11. 

Description. — Shell  small,  subcircular  in  outline,  usually  a  little  wider 
than  long  but  sometimes  longer  than  wide,  sublenticular  to  subglobular 
in  form,  the  valves  subequally  convex,  the  greatest  width  near  the  mid- 


4:5(i  MississilMMAN   BBACHIOPODA 

length,  the  hinge-line  much  shorter  than  the  greatest  width  of  the  shell, 
the  cardinal  extremities  rounded.  The  dimensions  of  two  nearly  perfect 
specimens  are:  length  of  pedicle  valve  9.6  nun.  and  S.S  mm.,  length  of 
brachial  valve  8.4  mm.  and  7.(i  mm.,  width  10.5  mm.  and  9.7  mm.,  thick- 
ness 5.3  mm.  and  (>.:l  mm.,  length  of  hinge-line  4.1  mm.  and  4  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
rather  abruptly  to  the  cardinal  margin  and  more  gently  to  the  lateral  and 
anterior  margins,  sometimes  slightly  compressed  towards  the  cardinal  ex- 
tremities; no  mesial  sinus  present  other  than  the  median  furrow  between 
the  plications  of  the  valve;  the  beak  rather  small,  blunt  at  the  extremity, 
moderately  incurved,  pierced  by  a  small  subcircular  foramen;  cardinal 
area  small,  broadly  triangular  in  outline,  gently  arched,  lying  in  nearly 
the  plane  of  the  valve,  its  lateral  margins  sharply  defined;  the  delthyrium 
broadly  triangular,  occupying  nearly  one-half  the  width  of  the  cardinal 
area  along  the  hinge-line,  its  apex  connecting  with  the  foramen  which 
encroaches  entirely  upon  the  beak  of  the  valve,  closed  by  a  pair  of  del- 
tidial  plates;  surface  of  the  valve  marked  by  from  six  to  twelve  strong, 
rounded,  simple  plications  which  are  separated  by  deep,  rounded  grooves 
about  equal  in  width  or  a  little  wider  than  the  plications  themselves,  the 
two  median  plications  the  strongest,  the  lateral  ones  becoming  successively 
smaller  towards  the  cardinal  extremities,  the  outermost  ones  sometimes 
becoming  almost  obsolete. 

Brachial  valve  more  uniformly  convex  than  the  pedicle,  the  greatest 
depth  near  the  middle,  usually  slightly  compressed  towards  the  cardinal 
extremities ;  the  beak  incurved  and  coming  in  contact  with  the  basal  mar- 
gin of  the  pseudodeltidiuni ;  plications  alternate  with  those  of  the  opposite 
valve  and  entirely  similar  to  them. 

Tn  addition  to  the  plications  both  valves  are  marked  by  concentric  lines 
of  growth  of  variable  strength  and  distribution.  Shell  structure  minutely 
punctate. 

Remarks. — This  species  is  rather  widespread  in  its  geographical  distri- 
bution in  the  Mississippi  valley,  in  the  faunas  of  the  late  Kinderhook,  and 
perhaps  passes  over  into  the  Burlington  limestone.  It  may  be  easily 
recognized  by  its  strong  plications,  and  is  not  closely  similar  to  any  other 
shell  in  these  faunas.  It  is  rather  variable  in  several  particulars,  especi- 
ally in  the  convexity  of  the  valves  and  consequent  globosity  of  the  shell, 
and  in  the  number  of  plications.  Because  of  its  variability  the  species 
has  been  described  under  several  names,  but  a  careful  examination  of  as 
many  specimens  as  possible  has  led  to  the  conclusion  that  the  differences 
observed  are  not  constant  and  are  not  even  of  varietal  importance,  and 
that  all  the  forms  belong  to  a  single  species. 

Horizon. — Kinderhook. 


EUMETRIA  437 

Genus  EUMETRIA  Hall 

Description. — Shells  small  or  of  medium  size,  subovate  in  outline,  the 
hinge-line  very  short,  the  valves  subequally  convex,  marked  by  fine, 
simple,  rounded  or  suhangular  radiating  plications.  Shell  structure  very 
minutely  and  closely  punctate.  Pedicle  valve  with  a  prominent,  incurved 
umbo,  perforated  at  its  apex  by  a  large,  subcircular  foramen  which  is  in 
contact  with  the  delthyrium  only  at  its  apex ;  the  cardinal  area  small, 
but  sharply  defined,  its  lateral  margins  abruptly  elevated  above  the  sur- 
face of  the  valve  on  either  side,  the  delthyrium  occupying  the  greater  part 
of  the  area,  closed  by  the  pseudodeltidium.  Internally  the  hinge-teeth 
are  of  moderate  size,  not  supported  by  dental  lamellae,  the  muscular 
impressions  inconspicuous,  being  only  rarely  sufficiently  impressed  to 
leave  any  suggestion  whatever  of  their  presence.  Brachial  valve  with 
the  cardinal  extremities  usually  compressed  to  form  minute  auriculations ; 
internally  the  hinge-plate  is  a  complicated  structure  consisting  of  a  pos- 
terior and  an  anterior  part,  extending  in  opposite  directions  from  the 
central  portion,  which  joins  the  two  socket  walls,  the  posterior  part  con- 
sists of  a  crescentic  process  whose  horns  make  nearly  a  semi-circle  and 
extend  backward  into  the  umbonal  region  of  the  pedicle  valve,  the  concave 
margin  of  the  crescent  lying  against  the  inner  surface  of  the  pseudodel- 
tidium of  the  opposite  valve,  the  tips  of  the  crescent  raised  away  from 
the  inner  surface  of  the  shell.  The  anterior  part  of  the  hinge-plate  is 
connected  with  the  median  part  by  a  narrow,  thickened,  median  band ; 
it  consists  of  a  long,  narrow,  concave  or  spoon-shaped  central  process 
with  sharply  elevated  edges,  these  marginal  ridges  being  produced  an- 
teriorly into  the  two  elongate,  slender,  and  nearly  vertical  crura,  the 
whole  being  supported  by  two  slightly  divergent,  upright  lamella?  which 
extend  to  the  floor  of  the  valve.  The  spiral  cones  approximate,  with 
eight  or  nine  volutions,  the  apices  directed  laterally,  the  jugum  posterior 
in  position,  regularly  curved  from  the  points  of  origin  on  the  primary 
lamellae  anteriorly  and  towards  the  interior,  from  its  central  point  a 
process,  bifid  at  the  extremity,  extends  towards  and  nearly  to  the  ex- 
tremities of  the  crura.  No  muscular  markings  have  been  observed  in 
this  valve. 

Remarks.— The  true  relations  of  this  genus  to  Acambona  have  not  been 
cleared  up,  and  because  of  the  rarity  of  examples  of  the  genotype  of 
Acambona,  it  may  be  a  long  time  before  the  relationships  of  the  two  genera 
can  be  determined.  There  are  no  characters  present  in  the  holotype  of 
Acambona  prima,  the  genotype  of  that  genus,  which  can  exclude  the  shell 
from  Eumetria. 


43S  MISSISSIPPI  AN  BRACHIOPODA 

BUMETBIA  ALTIBOSTBIS    (White) 

Plate  LXXV1,  Pigs.  7-11 

1862.     Retzia  (Acambonaf)  altirostris  White,  Proe.  Boston  Soc.  Nat.  Hist., 

vol.  9,  p.  28. 
1.897.     Eumetria   (f)   altirostris  Schuchert,  Synop.  Am.   Poss.  Braeh..  p. 

222. 
1900.    Eumetria  altirostris  Weller,  Trans.  St.  Louis  Acad.  Sci.,  voi.  10, 

p.  74.  pi.  2,  figs.   18-19. 

Description. — Shell  of  medium  size  or  smaller,  subovate  in  outline, 
longer  than  wide,  the  greatest  width  anterior  to  the  middle,  the  lateral 
margins  diverging  in  nearly  straight  lines  from  the  beak  to  nearly  the 
line  of  greatest  width,  the  anterior  and  antero-lateral  margins  describing 
a  nearly  semicircular  curve,  the  hinge-line  very  short.  The  dimensions  of 
a  nearly  complete,  large  individual  are:  length  of  pedicle  valve  23.5  mm., 
length  of  brachial  valve  20  mm.,  greatest  width  20.5  mm.,  thickness  14 
nun.,  length  of  hinge-line   ±5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbonal  region 
prominent  and  projecting  notably  beyond  the  hinge-line,  the  median  line 
of  the  valve  arcuate  or  curving  with  a  gradually  decreasing  curvature 
From  Hie  beak  to  the  front,  the  surface  curving  rather  abruptly  from  the 
median  portion  of  the  valve  to  the  lateral  margins,  and  posteriorly 
inflected  towards  the  cardinal  extremities ;  the  beak  prominent,  pointed 
and  incurved,  and  pierced  by  a  large,  subcircular  foramen  which 
encroaches  upon  the  umbonal  region  of  the  valve ;  the  cardinal  area 
small  and  arched,  its  lateral  margins  sharply  defined,  sloping  regularly 
from  the  sides  of  the  beak  to  the  cardinal  extremities;  in  the  median 
portion  of  the  valve  the  surface  is  flattened  along  an  indefinite  band 
extending  from  the  umbonal  region  to  the  front,  and  is  sometimes  de- 
pressed to  form  a  shallow,  ill-defined  median  sinus ;  the  surface  of  the 
valve  is  marked  by  from  19  to  21  simple,  depressed,  rounded  plications 
which  increase  gradually  in  size  in  passing  from  the  beak  to  the  margin, 
sometimes  a  plication  much  narrower  than  those  on  either  side  is  inter- 
calated along  the  median  line  at  near  the  mid-length  of  the  shell,  and 
continues  to  the  front  margin. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  beak  extending  a  little  beyond  the  hinge-line 
posteriorly,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  and  postero-lateral  margins,  the  median  portion  sometimes  a 
little  flattened  along  an  indefinite  band  extending  from  the  middle  of 
the  shell  to  the  anterior  margin,  but  never  elevated  into  a  distinct  mesial 
fold ;  the  surface  marked  by  plications  similar  in  form  and  number  to 
those  of  the  opposite  valve. 


EUMETRIA  439 

The  shell  structure  is  probably  punctate,  although  this  cannot  be  de- 
termined from  any  of  the  specimens  examined. 

Ui  marls. — The  minute  surface  markings  and  the  shell  structure  of  this 
species  cannot  be  determined  from  any  of  the  specimens  which  have  been 
examined,  because  of  their  condition  of  preservation  as  more  or  less 
modified  casts  in  a  fine-grained  sandstone.  In  a  few  cases  some  more  or 
less  indefinite,  concentric  lines  of  growth  are  retained,  but  for  the  most 
part  the  specimens  are  essentially  smooth,  aside  from  the  plications. 
Neither  the  characters  of  the  brachidium  nor  the  peculiar  characters  of 
the  hinge  of  Eumetria  have  been  observed  in  this  species,  and  unless 
individuals  in  a  different  condition  of  preservation  than  those  at  hand 
are  secured  at  some  future  time,  there  can  be  no  hope  of  certainly  deter- 
mining the  generic  relations  of  the  species.  So  far  as  external  form,  the 
characters  of  the  beak,  and  the  characters  of  the  cardinal  area  go,  there 
is  no  fundamental  difference  between  this  shell  and  the  true  species  of 
Eumetria  from  a  higher  horizon.  The  characteristic  features  of  this  species 
are  found  in  the  broad  plications,  which  are  less  in  number  than  in  any 
other  species  except  E.  acuticosta,  but  which  differ  from  that  species  in 
being  flat  and  rounded  instead  of  acutely  angular;  the  shell  also  has  a 
greater  tendency  to  develop  an  undefined  mesial  sinus  in  the  pedicle  valve 
than  any  of  the  other  species,  and  the  shell  is  usually  somewhat  more 
pointed  posteriorly.  The  small,  intercalated,  median  plication  which  is 
sometimes  present  in  specimens  of  this  species  is  also  a  character  differ- 
ent from  that  in  any  of  the  other  species. 

The  relationship  of  this  species  to  the  genus  Acambona,  and  indeed  the 
relationship  of  the  genus  Eumetria  to  Acambona,  is  quite  uncertain.  Ex- 
ternally the  two  genera  are  essentially  alike,  and  although  some  of  the  in- 
ternal  characters  of  Acambona  have  been  described  as  being  entirely  differ- 
ent from  similar  parts  of  Eumetria,  yet  authentic  specimens  of  Acambona 
are  so  rare  that  it  is  most  difficult  to  secure  material  from  which  to  really 
determine  its  essential  characters,  and  it  is  not  yet  entirely  certain  that 
the  structures  in  Acambona  have  been  correctly  interpreted,  or  that  there 
is  really  an  essential  generic  difference  between  it  and  Eumetria.  If  these 
two  genera  should  at  some  future  time  be  proven  to  be  synonymous,  the 
name  Eumetria  would  have  to  give  place  to  Acambona  which  has  several 
years  priority. 

Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 

Eumetria  osagensis  (Swallow) 

Plate  LXXVI,  Fig.  12 

1860.     Betzia  osagensis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  1,  p.  653. 
1894.     Eumetria?  osagensis  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt. 
2,  pi.  37,  figs.  7-9. 


440  M1SK1SSIIMMAN    BRACHI0P0DA 

1894.  Retzia  .'  osageiisis  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  !)4. 

1895.  Acambona  .'  osagt  nsis  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi. 

51,  figs.  38,  39. 

Description.  Shell  of  medium  size,  Longer  than  wide,  the  hinge-lii>c 
very  short,  subovate  in  outline,  the  greatesl  width  anterior  to  the  middle 
of  the  shell,  the  lateral  margins  diverging  from  the  beak  in  nearly  straight 
lines  almost  to  the  line  of  greatest  width  of  the  shell,  the  anterior  and 
antero-lateral  margins  describing  a  nearly  semicircular  curve.  The  di- 
mensions of  the  type  specimen  as  given  by  Swallow  are:  length  30.5  mm., 
width  23.8  mm.,  thickness  18.8  mm.  The  dimensions  of  an  imperfect, 
somewhat  crushed  example  are:  length  of  pedicle  valve  23  mm.,  length 
of  brachial  valve  20  mm.,  greatest  width  21.5  mm. 

Brachial  valve  most  convex  posterior  to  the  middle,  the  umbo  prom- 
inent and  projecting  notably  beyond  the  hinge-line,  the  surface  of  the 
valve  arched  from  beak  to  front  along  the  median  line,  somewhat  flat- 
tened towards  the  front,  the  curvature  of  the  surface  from  the  umbonal 
region  towards  the  postero-lateral  margins  is  rather  abrupt,  towards  the 
cardinal  extremities  becoming  inflected;  the  beak  is  prominent  and  in- 
curved, and  is  perforated  by  a  large,  circular  foramen  which  encroaches 
upon  the  umbonal  region;  the  cardinal  area  is  small  and  arched,  its  lateral 
margins  are  defined  and  slope  from  the  sides  of  the  beak  to  the  cardinal 
extremities. 

Brachial  valve  less  convex  than  the  pedicle,  the  greatest  convexity  pos- 
terior to  the  middle,  the  beak  somewhat  projecting  beyond  the  hinge-line, 
the  surface  curving  abruptly  from  the  umbonal  region  to  the  cardinal  ex- 
tremities and  to  the  postero-lateral  margins,  the  curvature  more  gentle 
anteriorly  and  antero-laterally. 

Each  valve  marked  by  about  50  fine,  simple,  flattened,  radiating  plica- 
tions separated  by  narrow  grooves.  The  shell  structure  minutely  and 
finely  punctate. 

Remarks. — This  is  an  exceedingly  rare  shell  in  the  Chouteau  limestone, 
and  only  a  single,  imperfect,  and  somewhat  crushed  specimen  has  come 
under  the  observation  of  the  writer.  It  is  essentially  impossible  to  point 
out  any  characters  by  which  the  species  can  be  separated  from 
E.  vcnieuiUaiiii  or  E.  vera.  The  number  of  plications  being  about  50  is 
perhaps  more  nearly  like  E.  verneuiliana.  but  the  apparent  shape  of  the 
shell,  with  its  greatest  width  in  front  of  the  middle,  is  more  like  E.  vera. 
Upon  the  specimen  which  has  been  studied  the  plications  of  the  shell  are 
apparently  more  sharply  marked  upon  the  exfoliated  portions  of  the  sur- 
face, and  upon  one  small  area,  which  is  apparently  in  its  natural  condition, 
no  plications  are  discernable.  It  is  possible  that  this  may  prove  to  be  an 
essential  feature  of  the  species,  but  to  determine  this  the  examination  of 
more  material  is  desirable. 


EUMETRIA  441 

The  reference  of  this  species  to  the  germs  Eumetria  may  he  incorrect, 
hut  there  is  no  way  to  determine  from  the  material  available  whether  it  is 
a  member  of  this  genus  or  of  Acambona.  It  has  been  referred  to  both 
genera  in  the  past,  but  never  upon  sufficiently  well  founded  evidence. 

Horizon. — Chouteau  limestone. 

EUMETRIA   PERSTRIALIS    Rowley 

Plate  LXXV1,  Figs.  4-6 

1900.     Eumetria  perstriaMs  Rowley,  Am.  Geol.,  vol.  25,  p.  266,  pi.  5,  figs. 
28-30. 

Description. — Shell  small,  longer  than  wide,  ovate-sub euneate  in  out- 
line, the  greatest  width  anterior  to  the  mid-length,  the  long  postero- 
lateral margins  nearly  straight  and  meeting  at  the  beak  in  an  angle  of 
about  57  degrees,  the  antero-lateral  margins  regularly  rounded  into  the 
less  curved,  subtruncate  anterior  margin.  The  dimensions  of  the  holo- 
type are :  length  of  pedicle  valve  10  mm.,  length  of  brachial  valve  8.9  mm., 
greatest  width  7.2  mm.,  thickness  6  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  from  the  point  of  greatest  convexity  to  the  postero-lateral  mar- 
gins and  becoming  a  little  inflected  to  the  cardinal  extremities,  curving 
with  a  long,  gently  convex  slope  to  the  anterior  margin  and  with  a 
shorter,  more  strongly  convex  curvature  to  the  beak  ;  mesial  sinus  or  fold 
obsolete;  the  beak  rather  large  and  prominent,  projecting  notably  beyond 
that  of  the  opposite  valve,  pierced  by  a  large  foramen  which  encroaches 
upon  the  umbonal  region  of  the  valve,  the  delthyriuni  closed  by  deltidial 
plates;  cardinal  area  very  small,  scarcely  greater  than  the  delthyriuni. 

Brachial  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  curving  abruptly  to  the  postero-lateral  margins,  sloping  with  a 
long,  gently  convex  curvature  to  the  anterior  margin  and  with  a  shorter 
and  more  strongly  convex  curvature  to  the  beak;  mesial  fold  or  sinus  ob- 
solete ;  the  beak  rather  strongly  incurved  beneath  the  psetidodeltidium  of 
the  opposite  valve. 

Surface  of  both  valves  marked  by  tine,  simple,  radiating  plications, 
three  or  four  of  which  occupy  the  space  of  one  millimeter  at  the  front  of 
the  shell,  the  entire  number  recognizable  being  about  42,  in  the  posterior 
half  of  the  shell  these  plications  become  so  fine  that  the  shell  appears  to 
be  smooth  except  when  examined  under  a  lens.  A  little  posterior  to  the 
middle  a  rather  strong  line  of  growth  marks  each  valve  in  the  holotype, 
with  a  somewhat  smaller  line  between  it  and  the  umbo,  other  concentric 
markings  obsolete. 

Remarks.— A  single  example  of  this  species,  the  holotype,  has  been  ex- 
amined. Its  internal  characters  are  unknown  so  it  is  not  possible  to  de- 
termine whether  or  not  it  possesses  the  essential  characters  of  Eumetria  or 


442  Mississippi  AX    BRACHIOPODA 

of  Acambona,  if  these  two  genera  should  prove  to  be  distinct.  It  differs 
i  null  all  oilier  species  of  Ewrru  tria  m  its  more  narrowly  ovate  outline,  and  in 
its  exceedingly  line  radiating  plications.  In  these  characters  it  much 
more  closely  resembles  Acambona  prima,  indeed,  in  all  essential  features  it 
has  every  appearance  of  being  a  diminutive  example  of  that  species,  and 
it  should  perhaps  be  so  considered.  The  satisfactory  interpretation  of 
these  rare  forms,  however,  must  he  deferred  until  more  abundant  mate- 
rial is  available  for  study. 

Horizon. — Lower  Burlington  white  chert. 

EUMETRIA   VERNEUILANA    (Hall) 

I 'I  at.'  LXXVI,  Pigs.  18-24 

1852.     Terebratula  serpentaria  .'  Owen.  Geol.  Rep.  Wis.,  Iowa  and  Minn., 

tab.  3A,  ag.  1:5. 
lS.>t;.     h'(l:ia  Y<  nu  uilana  Mall,  Trans.  Albany  Inst.,  vol.  4,  p.  9. 
1858.     h'clzin   rcnii  uilana   Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  657,  pi.  23, 

figs.  la-d. 

1882.  Eumetria    Y<rn<  uilana  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol. 

1,  p.  50,  pi.  (i,  figs.  28-30. 

1883.  Eumetria  vemeuiliana  Hall,  12th  Rep.  Geol.  Surv.  Ind.,  p.  335,  pi. 

29,  figs.  28-30. 

1884.  Kctzia  Vcrncuitiana  Walcott,  Pal.  Eureka  Dist,  p.  220,  pi.  7,  tigs. 

5-5a. 
1894.     Eumetria  \'<  rnt  wiliana  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt. 

2,  pi.  37,  figs.  1-4,  6,  10. 

1894.  Betzia  verve uiliana  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  95. 

1895.  Eumetria  Vemeuiliana  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 

pi.  51,  figs.  13-26,  34,  35;  pi.  83,  figs.  26-27. 
1897.     Eumetria  verncuilana   Weller,    Trans.   N.   Y.   Acad.   Sci.,   vol.    16, 

p.  259. 
1899.     Eumetria  vemeuiliana  Girty.  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p. 

560,  pi.  68,  figs.  12a-b. 

1903.  Eumetria  marcyi?  Girty,  U.  S.  Geol.  Survey,  Prof.  Paper,  No.  16,  p 

303. 

1904.  Eumetria  marcyi  Girtv,  Prof.  Paper  U.  S.  Geol.  Survey,  No.  21,  p 

49,  pi.  10,  figs.  15-17. 
1906.     Eumetria  marceyi  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1319, 

pi.  22,  figs.  28-30. 
1911.     Eumetria  marcyi  Girty,  Bull.  U.  S.  Geol.  Survey,  No.  439,  p.  77, 

pi.  8,  fig.  10. 
1911.     Eumetria  marcyi  Morse,  Proc.  Ohio  State  Acad.  Sci.,  vol.  5,  p.  386, 

fig.  14. 
Description. — Shell  small,  longer  than  wide,  the  greatest  width  near  the 
mid-length  of  the  shell,  ovate  in  outline,  the  lateral  margins  diverging 
from  the  beak  at  varying  angles  in  nearly  straight  lines  or  with  slightly 
convex  curvature  to  the  line  of  greatest  width  of  the  shell,  in  front  of 
this  line  the  outline  is  subsemicircular  with  sometimes  a  slight  straighten- 
ing or  truncation  of  the  margin  at  the  anterior  extremity,  the  hinge-line 


EUMETRIA  443 

very  short.  The  dimensions  of  two  individuals  are :  length  of  pedicle 
valve  19  mm.  and  21  mm.,  length  of  brachial  valve  16  mm.  and  18  mm., 
greatest  width  18  mm.  and  19  mm.,  thickness  11  mm.  and  14  mm.,  length 
of  hinge-line  5  mm.  and  5  mm. 

Pedicle  valve  more  or  less  strongly  convex,  the  greatest  convexity  pos- 
terior to  the  middle,  the  nmbonal  region  prominent  and  projecting  not- 
ably beyond  the  hinge-line,  the  surface  curving  from  the  umbonal  region 
to  the  anterior  with  a  regularly  decreasing  convexity,  laterally  the  curva- 
ture becomes  more  abrupt  towards  the  cardinal  extremities;  towards  the 
cardinal  margin  the  surface  is  inflected  and  not  infrequently  slightly 
aurieulate  at  the  cardinal  extremities;  the  beak  is  pointed,  strongly  in- 
curved, and  is  pierced  by  a  large,  subcircular  foramen  which  encroaches 
notably  upon  the  umbonal  region,  only  the  margin  of  it  occupying  the 
apical  portion  of  the  delthyrium ;  the  cardinal  area  is  very  small,  arched, 
the  lateral  margins  usually  sharply  defined  and  sloping  in  nearly  straight 
lines  from  the  sides  of  the  beak  to  the  cardinal  extremities,  the  delthy- 
rium closed  by  a  pseudodeltidium ;  the  mesial  sinus  is  obsolete,  but  in  some 
individuals  there  is  a  slight,  indefinite  flattening  in  the  anterior  median 
portion  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  convex- 
ity posterior  to  the  middle;  the  beak  pointed  and  very  slightly  projecting 
beyond  the  hinge-line ;  the  surface  curving  from  the  beak  to  the  anterior 
margin  with  gradually  lessening  curvature,  laterally  the  curvature  be- 
comes more  abrupt  towards  the  cardinal  extremities  where  the  siirface  is 
compressed  to  form  small  auriculations  which  are  larger  than  those  of  the 
pedicle  valve  ;  along  the  median  portion  of  the  valve  the  surface  is  slightly 
and  indefinitely  flattened  towards  the  front  of  the  shell,  but  no  mesial 
fold  is  developed,  the  flattening,  however,  is  usually  more  marked  than 
that  of  the  pedicle  valve. 

The  surface  of  both  valves  is  marked  by  fine,  simple,  rounded,  nearly 
uniform,  radiating  plications,  separated  by  furrows  narrower  than  the 
plications  themselves;  each  valve  bears  from  42  to  55  of  these  plications, 
the  more  usual  number  being  between  46  and  50.  The  shell  structure  is 
minutely  punctate. 

Remarks. — This  species  exhibits  great  variation  in  size,  in  the  propor- 
tional dimensions  of  length  and  width,  and  in  the  convexity  of  the  valves. 
Some  examples  attain  a  larger  size  than  either  of  those  whose  dimensions 
have  been  given  above;  a  smaller  size  is  the  more  usual,  however,  although 
the  specimens  exhibit  the  characteristics  of  adult  shells.  Occasionally 
the  valves  become  strongly  ventricose,  especially  in  old  individuals. 

In  his  bibliographic  list  Schuchert1  has  included  this  form  as  well  as 
E.  vera  Hall  and  E.  vera  var.  cosiata  Hall,  as  synonyms  under  E.  marcyi 

l  Bull.  U.  S.  Geol.  Survey,  No.  87,  p.  222.     (1897.) 


-144  mississiim'IAN    BEACHIOPODA 

Shumard.  The  originals  of  Shumard 's  species  were  from  Washington  and 
Crawford  Counties,  Arkansas,  and  have  evidently  been  lost,  and  his 
illustrations  are  so  imperfecl  that  they  can  scarcely  be  recognized.  The 
only  tangible  character  mentioned  in  the  original  description  is  the 
number  of  plications,  which  are  stated  to  be  from  34  to  38  upon  each 
valve,  a  number  which  would  correspond  with  examples  of  E.  costata. 
tf  these  different  forms  are  recognized  as  distinct,  as  is  done  here, 
Shumard 's  name  cannot  he  considered  as  having  priority  over  E. 
verneuiliana,  and  if  \i^-<\  at  all  must  be  used  as  a  substitute  for  E.  costata. 
Considering  the  uncertainty  which  must  exist  in  the  absence  of  the  type 
specimens,  as  to  what  E.  marceyi  really  is,  it  seems  best  to  drop  that  name 
altogether  and  to  use  the  mimes  applied  by  Hall,  which  were  clearly 
defined  and  wwf  illustrated  by  excellent  figures. 

Horizon. — Salem  limestone;  St.  Louis  limestone:  Chester  group. 

EUMETRIA    VERA     (Hall) 

Plate  LXXVI,  Figs.  13-17 

1858.     Retzia  vera  Hall,  Geol.  Iowa.  vol.  1,  pt.  2,  p.  704,  pi.  27,  fig.  3a. 
1894.     Eumetria    vera   Hall   and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 
pi.  37,  figs.  8,  12. 

1894.  Retzia  vera  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  95. 

1895.  Eumetria  vera  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  51, 

figs.  36,  37. 
1909.     Eumetria  marcyi  Bassler,  Va.  Geol.  Surv.,  Bull.  No.  II  A.,  pi.  29, 
figs.  4-5. 

Description. — Shell  of  medium  size,  longer  than  wide,  the  greatest  width 
anterior  to  the  mid-length  of  the  shell,  subovate  in  outline,  the  sides 
diverging  from  the  beak  anteriorly  in  nearly  straight  or  slightly  convex 
lines  to  the  line  of  greatest  breadth,  anteriorly  the  outline  is  sub- 
semicircular,  often  with  a  slight  straightening  of  the  anterior  margin, 
the  hinge-line  very  short.  The  dimensions  of  three  individuals  are : 
length  of  pedicle  valve  25.5  mm.,  20  mm.  and  19  mm.,  length  of  brachial 
valve  23.5  mm.,  17  mm.  and  17  mm.,  greatest  width  26  mm.,  19  mm.  and 
16  mm.,  thickness  16  mm.,  11  mm.  and  10  mm.,  length  of  hinge-line  6.5 
mm.,  5.5  mm.  and  ±4.5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbonal  region 
prominent  and  projecting  posteriorly  beyond  the  hinge-line,  the  surface 
curving  with  a  regularly  diminishing  curvature  from  the  beak  to  the 
anterior  margin,  the  curvature  gradually  becoming  more  abrupt  anter- 
iorly along  the  lateral  margins,  and  towards  the  cardinal  extremities 
becoming  inflected,  at  the  cardinal  extremities  the  surface  is  again 
slightly  deflected  to  form  a  pair  of  minute  auriculations  which  are  some- 
times nearly  or  quite  obsolete;  the  beak  is  large,  prominent  and  incurved, 
and  is  pierced  by  a  large  circular  foramen   which  encroaches   notably 


EUMETRIA  t45 

upon  the  umbonal  region,  only  rue  margin  oi  n  oemg  in  contact  with  the 
delthyrium ;  cardinal  area  small,  arched,  the  lateral  margins  sharply 
defined,  sloping  from  the  sides  of  the  beak  in  nearly  straight  lines  to  the 
cardinal  extremities,  the  delthyrium  closed  by  a  pseudodeltidium ; 
median  portion  of  the  valve  not  depressed  in  a  sinus  but  sometimes 
slightly  flattened  along  an  indefinite  mesial  band. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  beak  extending  slightly  beyond  the 
hinge-line  posteriorly,  the  surface  curving  rather  abruptly  from  the 
umbonal  region  towards  the  cardinal  extremities,  but  before  reaching 
the  margin  it  is  deflected  to  form  a  pair  of  small,  nearly  flat  auriculations 
a  Jittle  more  conspicuous  than  those  of  the  opposite  valve,  forward  from 
the  cardinal  extremities  along  the  lateral  margins  to  the  anterior  margin 
the  curvature  becomes  gradually  more  gentle;  the  median  portion  of  the 
valve  is  sometimes  slightly  flattened  along  an  indefinite  mesial  band  but 
is  not  elevated  in  a  fold. 

Both  valves  are  marked  by  regular,  simple,  rounded,  nearly  uniform, 
radiating  plications  which  are  so  fine  as  to  be  almost  indistinguishable 
at  tbe  beak,  but  increase  gradually  in  strength  with  the  growth  of  the 
shell.  The  number  of  these  plications  is  usually  between  42  and  48 
on  each  valve.  Lines  of  growth  are  inconspicuous  or  wanting.  The  shell 
structure  minutely  punctate. 

Remarks. — This  species  is  closely  allied  to  E.  verneuilana  and  has  some- 
times been  considered  as  a  synonym  of  that  species.  There  seem  to  be 
some  reasons,  however,  for  its  recognition  under  a  distinct  name,  but 
whether  this  designation  should  be  considered  as  of  specific  or  varietal 
rank  is  largely  a  matter  of  personal  opinion.  There  seems  to  the  writer 
to  be  little  utility  in  using  three  names  to  distinguish  a  certain  form, 
and  if  it  has  characters  sufficiently  distinct  to  allow  its  being  separated 
from  another,  it  seems  worth  while  to  designate  it  by  a  specific  name. 
Eumctria  vera  differs  from  E.  verneuilana  in  attaining  a  larger  size, 
in  having  a  somewhat  smaller  maximum  number  of  plications,  and  in 
the  more  anterior  position  of  the  greatest  width  of  the  shell.  In  addition 
to  these  characters,  no  examples  have  been  observed  to  attain  so  great  a 
convexity  as  is  sometimes  developed  in  E.  verneuilana. 

Horizon.  —  Chester  group. 

EUMETRIA   COSTATA    (Hall) 

Plate  LXXVI,  Pigs.  25-29 

1858.     Retzia  vera  var.  costata  Hall,  Geol.  Iowa,  vol.  1.  pt.  2,  p.  704,  pi.  27, 

figs.  3a-b. 
1894.     Eumetria  vera  var.  costata  Hall  and  Clarke.  Int.  to  Study  of  Brach., 

pt.  2,  pi.  37,  figs.  5,  11. 


446  MISSISSIPPIAN   BRACHIOPODA 

L895.     Eum<  triq  vera  var.  castata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2, 
pi.  51,  Bgs.  27-33. 

Description.-  Shell  attaining  a  medium  size,  longer  than  wide,  the  hinge- 
lint'  very  short,  the  greatest  width  antei'ior  to  the  middle,  suhovate  in 
outline,  the  Lateral  margins  diverging  from  the  beaks  nearly  to  the  line 
dl'  greatest  width  in  straighl  or  slightly  convex  lines,  anteriorly  the 
outline  is  subsemicircular,  sometimes  with  a,  slight  straightening  of  the 
margin  in  the  center.  The  dimensions  of  two  individuals  are:  length 
of  pedicle  valve  ■'!<>  mm.  and  27  mm.,  Length  of  brachial  valve  26  mm.  and 
23.5  mm.,  greatest  width  28  mm.  and  23  mm.,  thickness  16  mm.  and  15 
mm.,  length  of  hinge-line  6  mm.  and  7  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbonal  region 
projecting  notably  beyond  the  binge-line;  the  curvature  of  the  surface 
from  the  beak  to  the  anterior  margin  has  a  regularly  decreasing  convexity, 
the  convexity  to  the  lateral  margins  becoming  gradually  more  abrupt 
anteriorly;  towards  the  cardinal  extremities  the  surface  is  inflected,  and 
at  the  cardinal  extremities  the  surface  is  again  deflected  to  form  a  pair 
of  minute,  sometimes  almost  obsolete,  auriculations ;  the  beak  is  prom- 
inent and  incurved,  and  is  pierced  by  the  large,  subcircular  foramen, 
which  encroaches  notably  upon  the  umbonal  region ;  the  cardinal  area 
small,  arched,  its  lateral  margins  sharply  defined,  sloping  regularly  from 
the  sides  of  the  beak  to  the  cardinal  extremities,  the  delthyrium  closed 
by  the  pseudo-deltidinm,  only  its  apex  being  in  contact  with  the  foramen; 
mesial  portion  of  the  valve  not  depressed  in  a  sinus,  but  sometimes  the 
surface  of  the  valve  is  flattened  along  an  undefined  mesial  band,  especially 
towards  the  front. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  beak  projecting  slightly  beyond  the 
hinge-line,  the  surface  curving  somewhat  abruptly  from  the  umbonal 
region  towards  the  cardinal  extremities,  but  again  deflected  just  before 
it  reaches  these  extremities  to  form  a  pair  of  small  auriculations  a  little 
more  conspicuous  than  those  of  the  pedicle  valve;  anteriorly  from  the 
beak  to  the  front  of  the  valve  the  surface  describes  a  gradually  decreasing 
convex  curve  and  laterally  the  curvature  becomes  gradually  more  convex 
in  passing  from  the  anterior  margin  towards  the  hinge  extremities. 

Each  valve  is  marked  by  from  30  to  40  regular,  simple,  depressed, 
rounded,  nearly  uniform,  radiating  plications,  which  increase  regularly 
in  size  in  passing  from  the  beak  to  the  front.  Growth  lines  are  either 
lacking  or  are  inconspicuous.     The  shell  structure  is  minutely  punctate. 

Remarks.  —  This  shell  was  originally  described  as  a  variety  of  E.  vera, 
and  has  sometimes  been  considered  along  with  that  species,  as  synonymous 
with  E.  verneuilana.  It  is  not  improbable  that  all  of  these  forms 
might  be  shown  to  be  united  by  intergradations,  yet  it  seems  advisable 


EUMETRIA  447 

to  retain  their  separate  names  as  applied  by  Hall,  considering 
costata  as  of  equal  rank  with  the  others,  however,  and  not  as  a  variety 
under  E.  vera.  Each  form  possesses  its  individual  characteristics  and  the 
number  of  individuals  possessing  those  characteristics  is  much  greater  than 
those  with  intermediate  characters.  E.  costata,  perhaps,  attains  a  larger 
size  than  any  of  the  others,  but  in  general  outline  it  is  not  essentially 
different  from  E.  vera,  having  its  greatest  width  anterior  to  the  middle 
of  the  shell.  The  distinctive  feature  of  the  form  is  its  coarser  plications, 
about  35  being  nearly  the  normal  number,  while  the  other  two  species, 
although  usually  smaller  shells,  have  usually  45  or  more  plications. 
Horizon. — Chester  group. 

EUMETRIA  ACUTICOSTA  11.  sp. 

Plate  LXXVI,  Figs.  30-34 

Description. — Shell  small,  hinge-line  very  short,  length  and  breadth 
nearly  equal,  the  greatest  width  near  the  mid-length  of  the  shell,  the 
lateral  margins  diverging  from  the  beak  anteriorly  nearly  to  the  line 
of  greatest  width  of  the  shell,  the  anterior  and  antero-lateral  margins 
subsemicircular.  The  dimensions  of  a  perfect  specimen  are :  length  of 
pedicle  valve  16.3  mm.,  length  of  brachial  valve  14  mm.,  greatest  width 
16  mm.,  thickness  10.5  mm.,  length  of  hinge-line  4  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  umbo  prominent 
and  projecting  notably  beyond  the  hinge-line,  the  surface  curving  from 
the  beak  to  the  anterior  margin  with  a  regularly  decreasing  convex 
curvature,  towards  the  lateral  margins  the  curvature  becomes  gradually 
more  abrupt  in  passing  from  the  anterior  margin  posteriorly;  towards 
the  cardinal  extremities  the  surface  becomes  inflected  and  at  the  cardinal 
extremities  it  is  again  deflected  to  form  a  pair  of  minute  auriculations ; 
the  beak  is  prominent,  incurved,  and  is  pierced  by  a  large,  circular  fora- 
men which  encroaches  upon  the  umbonal  region ;  the  cardinal  area  small, 
arched,  sharply  defined,  the  cardinal  margins  sloping  regularly  from 
the  sides  of  the  beak  to  the  cardinal  extremities ;  the  valve  is  without 
median  sinus,  the  median  portion  not  even  being  flattened  as  it  is  in 
some  members  of  the  genus. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  beak  projecting  slightly  beyond  the 
hinge-line,  the  surface  curving  rather  abruptly  from  the  umbonal  region 
towards  the  cardinal  margin,  the  curvature  becoming  gradually  more 
gentle  in  passing  anteriorly  along  the  lateral  margins  to  the  anterior 
extremity,  along  the  median  line  of  the  valve  from  the  beak  anteriorly, 
the  surface  describes  a  regularly  diminishing  convex  curve,  at  the  car- 
dinal extremities  the  surface  of  the  valve  is  deflected  to  form  a  pair  of 
minute  auriculations. 


44S  Mississii'i'iAN    BRACHIOPODA 

Each  valve  is  marked  by  about  22  sharply  angular,  nearly  uniform 

simple,  radiating  plications  which  increase  gradually  iii  size  in  passing 
limn  the  beak  towards  the  margin.  Conspicuous  growth  lines  are  obsolete 
upon  the  type  .specimen,  but  exceedingly  minute,  concentric  stria-  may  be 
detected  upon  some  portions  of  the  shell.  The  shell  structure  is  minutely 
punctate. 

Ii'<  marks.-  This  species  differs  primarily  from  the  other  recognized 
members  of  the  genus  in  its  much  coarser  and  deeper,  strongly  angular 
plications.  The  shell  is  also  proportionally  broader  than  is  usually  the 
case  with  individuals  of  other  species,  it  being  nearly  equal  in  length 
and  breadth. 

Horizon. — <  Tester  group. 

Genus  ACAMBONA  White 

Description. — Shells  of  medium  size  or  larger,  subovate  in  outline,  the 
binge-line  very  short,  the  valves  subequally  convex,  marked  by  fine, 
rounded,  simple  plications,  the  shell  structure  minutely  and  closely 
punctate.  Pedicle  valve  with  a  small  cardinal  area  having  its  lateral 
margins  sharply  defined  and  elevated  above  the  surface  of  the  valve  on 
either  side,  the  delthyrium  occupying  nearly  the  entire  cardinal  area, 
closed  by  the  pseudodeltidium ;  the  foramen  large,  subcircular,  encroach- 
ing wholly  upon  the  umbonal  region  of  the  valve.  Internally,  dental 
lamellae  are  apparently  absent,  no  other  internal  characters  recognizable 
in  the  genotype  except  the  presence  of  a  spiral  brachidium.  The  brachial 
valve  slightly  compressed  at  the  cardinal  extremities  to  form  minute 
auriculations,  the  internal  characters  not  preserved  in  the  genotype. 

Remarks.— The  essential  generic  characters  of  the  holotype  of  A.  prima, 
the  genotype  of  Acambona,  are  not  preserved,  and  so  far  as  this  specimen 
is  concerned,  there  is  no  reason  for  placing  it  in  any  genus  other  than 
Eumetria.  Hall  and  Clarke1  have  stated,  however,  that  members  of  the 
species  A.  prima  bear  "an  internal  pedicle-tube,  as  in  Rctzia  and  Hustedia, 
a  character  absent  in  Eumetria."  Specimens  of  this  species  are  exceedingly 
rare  and  only  the  holotype  has  been  available  to  the  writer  for  study, 
and  no  such  pedicle-tube  is  visible  in  that  specimen,  although  it  may  be 
present.  Until  further  information  concerning  the  genus  can  be  secured 
it  seems  best  to  allow  it  to  stand  with  the  genotype  as  the  single  repre- 
sentative, although  if  it  is  really  a  good  genus,  it  is  possible  that  some 
of  the  species  here  placed  in  Eumetria  may  be  eventually  transferred  to  it. 

l  Pal.  N.  Y.,  vol.  8,  pt.  2,  p.  119.     (1894.) 


ACAMBONA  449 


ACAMBONA  PRIMA   White 

Plate  LXXVI,  Figs.  1-3 
1862.     Acambona  prima  White,  Proc,  'Boston  Soe.  Nat.  Hist.,  vol.  9.  p.  27, 

figs.  1-2. 
(?)   1894.     Acambona  prima  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt. 

2,  pi.  37,  figs.  21-22. 
(?)   1895.     Acambona  prima  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi. 

51,  figs.  40-41. 

Description. — Shell  above  medium  size,  subovate  in  outline,  longer  than 
wide,  the  greatest  width  at  about  the  mid-length,  the  hinge-line  very 
short,  the  anterior  and  antero-lateral  margins  regularly  rounded,  the 
postero-lateral  margins  nearly  straight  or  slightly  convex,  meeting,  when 
projected  beyond  the  beak,  in  an  angle  of  about  67  degrees.  The  dimen- 
sions of  the  holotype,  a  somewhat  imperfect  and  distorted  specimen,  are : 
length  of  pedicle  valve  40  mm.,  length  of  brachial  valve  35  mm.,  greatest 
width  27.8  mm.,  thickness  ±21  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  ap- 
parently about  half  way  between  the  middle  and  the  beak,  the  median 
portion  of  the  valve  gently  convex  transversely,  the  surface  becoming 
more  abruptly  convex  as  it  approaches  the  lateral  margins,  and  becoming 
incurved  to  the  cardinal  extremities  and  to  the  postero-lateral  margins ; 
mesial  sinus  wanting ;  cardinal  area  very  small,  scarcely  reaching  beyond 
the  limits  of  the  delthyrinm,  sharply  defined  laterally,  its  lateral  margins 
sharply  elevated  from  the  postero-lateral  slopes  of  the  valve,  concave 
with  the  curvature  increasing  towards  the  beak,  the  delthyrinm  closed 
by  a  pseudodeltidium  in  its  upper  part,  the  lower  portion  occupied  by  the 
beak  of  the  opposite  valve ;  the  beak  sharply  pointed  and  strongly  in- 
curved, the  foramen  apparently  large  and  encroaching  entirely  upon  the 
umbonal  portion  of  the  valve,  not  in  contact  with  the  delthyrium  even  at 
its  apex. 

Brachial  valve  apparently  about  equally  convex  with  the  pedicle,  with 
the  greatest  convexity  near  or  posterior  to  the  middle,  the  surface  curving 
rather  abruptly  to  the  postero-lateral  margins,  less  abruptly  to  the  lateral 
and  more  gently  to  the  anterior  margin,  compressed  at  the  cardinal  ex- 
tremities to  form  minute  alations;  mesial  fold  or  shins  wanting;  beak 
pointed  and  incurved  beneath  the  margin  of  the  pseudodeltidium  of  the 
opposite  valve  and  filling  the  lower  portion  of  the  delthyrinm  of  that 
valve. 

Surface  of  each  valve  marked  by  about  90  simple,  depressed,  rounded, 
radiating  plications  which  become  obsolete  on  the  umbonal  portion  of  the 
valves,  being  clearly  defined,  indeed,  only  in  the  anterior  half  of  each 
valve,  not  over  fifty  of  the  plications  are  conspicuous,  about  20  on  each 

—15 


450  MISSISSIPPIAN    BRACHIOPODA 

side  along  the  postero-lateral  margins  being  very  faint  and  difficull  to 
distinguish,  the  largest  plications  at  the  front  margin  measure  about  1 
mm.  from  center  to  center.  The  plications  are  crossed  by  concentric  lines 
of  growth,  several  of  which  in  the  anterior  half  of  the  shell,  are  strongly 
marked  and  wrinkle-like  in  the  type.     The  shell  substance  punctate. 

Remarks. — The  present  description  of  this  species  has  been  based  upon 
the  holotype  now  preserved  in  (lie  White  Collection  at  the  University  of 
Michigan,  the  oidy  example  to  come  under  the  observation  of  the  writer. 
In  the  original  definition  of  the  genus  Acambona  no  mention  of  a  foramen 
in  the  pedicle  valve  is  made,  and  no  indication  of  such  an  opening  is 
shown  in  the  illustration  of  the  shell,  and  this  supposed  imperforate  con- 
dition of  this  valve  was  evidently  the  character  upon  which  the  genus 
was  primarily  based.  The  type  specimen  shows  a  large  opening  in  the 
umbonal  portion  of  the  pedicle  valve  just  back  of  the  beak  which  is  be- 
lieved to  be.  without  doubt,  a  Large  foramen.  The  margins  of  this  open- 
ing,  however,  arc  irregular  and  indicate  a  broken  condition  except  for  a 
short  distance  where  the  natural  border  of  the  foramen  is  clearly  present; 
because  of  this  condition.  While  evidently  interpreted  it  as  an  acci- 
dental fracture  of  the  shell.  The  remarkable  degree  of  encroachment  of 
the  foramen  upon  the  umbonal  region  of  the  valve,  so  that  it  is  entirely 
out  of  contact  with  the  apex  of  the  delthyrium,  tlms  allowing  the  apex 
of  the  beak  to  remain  sharply  pointed,  was  probably  another  reason  for 
White's  interpretation  of  the  opening  as  an  accidental  break.  With  the 
elimination  of  the  imperforate  beak  of  the  pedicle  valve,  there  remains 
no  external  character  of  more  than  specific  value  to  separate  this  shell 
from  members  of  the  genus  Eumetria.  It  has  been  shown  by  Hall  and 
Clarke,1  however,  that  a  calcareous  pedicle  tube  upon  the  inner  surface 
of  the  pseudodeltidium,  such  as  is  present  in  Retzia  and  Hustedia,  is 
wanting  in  Eumetria,  and  it  is  stated  by  these  same  authors2  that  such  a 
structure  is  present  in  Acanthoma  prima.  Hall  and  Clarke,  however,  had 
apparently  never  studied  the  holotype  of  the  species,  and  a  careful  ex- 
amination of  this  specimen  has  failed  to  demonstrate  either  the  presence 
or  the  absence  of  such  a  structure ;  under  the  circumstances  the  status 
of  the  genus  Acambona  must  remain  doubtful.  If  there  is  no  pedicle  tube 
present,  it  is  altogether  likely  that  this  species  is  not  generically 
different  from  the  shells  included  in  Eumetria,  in  which  case  the  name 
Acambona  must  take  precedence  over  Eumetria,  having  been  proposed  by 
White  in  1862,  one  year  previous  to  the  first  usage  of  Eumetria  by  Hall. 
But  if  a  pedicle  tube  is  really  present,  the  genus  is  doubtless  a  good  one. 
Because  of  the  extreme  rarity  of  examples  of  the  species,  it  may  be  long 
before  its  true  relations  can  be  satisfactorily  established,   but   for  the 

lPal.  N.  Y.,  vol.  8,  pt.  2,  pp.  115-119.     (1895.) 
2Loc.  ct.,  p.  119. 


HUSTEDIA  451 

present  it  seems  best  to  retain  the  genus  with  the  genotype   as   the  only 
representative. 

Horizon, — Burlington  limestone 

Genus  HUSTEDIA  Hall 

Description.- — Shells  small,  subovate  in  outline,  with  nearly  equally 
convex  valves,  marked  by  rather  coarse,  subangular,  simple  plications,  the 
shell  structure  punctate.  Pedicle  valve  with  a  prominent  umbo  perfor- 
ated at  its  apex  by  a  subcircular  foramen,  cardinal  area  small,  with 
sharply  defined  lateral  margins,  the  delthyrium  closed  by  the  pseudodel- 
tidium  and  in  contact  with  the  foramen  only  at  its  apex.  Internally  the 
inner  surface  of  the  pseudodeltidium  bears  a  split  tube  attached  by  its 
closed  side  to  the  deltidial  plates,  with  its  open  side  directed  towards  the 
interior  of  the  shell.  In  the  brachial  valve  the  hinge-plate  projects  con- 
siderably beyond  the  hinge-line  posteriorly,  being  recurved  into  the  urn- 
bonal  cavity  of  the  pedicle  valve,  the  upper  face  is  convex  and  elevated 
medially,  the  posterior  margin  sinuate  and  crescentic  with  the  horns  of 
crescent  very  short,  from  the  lateral  margins  of  the  plate  arise  a  pair  of 
strong  lobes  which  bear  the  erect,  slightly  recurved  crura.  At  the  base 
of  the  cardinal  process  and  in  the  median  line,  there  arises  a  free,  slender, 
ligulate  process  which  curves  upward  and  backward  with  a  somewhat  less 
curvature  than  the  hinge-plate,  and  rises  to  the  highest  point  attained  by 
the  latter ;  the  inner  surface  of  this  process  is  deeply  grooved  and  at  its 
base  it  is  supported  by  a  median  septum  which  extends  for  one-third  the 
length  of  the  valve.  The  spiral  cones  of  the  brachidium  and  the  jugum 
are  similar  to  those  of  Eumetria,  but  the  posterior  margins  of  the  coils  and 
the  jugum  are  fimbriated,  and  the  extremity  of  the  stem-like  process  from 
the  jugum  is  apparently  simple. 

Remarks.— The  genotype  of  Hustedia  is  the  Pennsylvanian  shell  H.  mor- 
moui,  and  the  description  of  the  internal  characters  of  that  shell,  given 
above,  has  been  taken  froml  the  work  of  Hall  and  Clarke.  Externally  these 
shells  differ  from  Eumetria  only  in  their  smaller  size  and  coarser  plications. 
The  internal  characters  of  H.  circularis  of  this  report  have  never  been 
determined,  and  the  species  is  placed  in  the  genus  Hustedia  only  because 
of  its  external  resemblance  to  the  genotype. 

Hustedia  circularis   (Miller) 
Plate  LXXVI,  Figs.  47-52 

1 892.     Retzia  circularis  Miller,   Adv.   Sheets  18th  Rep.   Geol.   Surv.   Ind., 

p.  62,  pi.  9,  figs.  32-34. 
1894.     Retzia  circularis  Miller,  18th  Rep.  Geol.  Surv.  Ind.,  p.  316,  pi.  9, 

figs.  32-34. 
1909.     Retzia  circularis   ?  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  317, 

pi.  12,  fig.  23. 


452  MISSISSIPPIAN    BRACHIOPODA 

Description. — Shell  very  small,  subglobular,  ovate  in  outline,  the  cardinal 
extremities  not  differentiated  from  the  general  curvature  of  the  outline, 
the  greatesl  width  near  the  mid-length,  the  binge-line  short,  ahout  two- 
lift  lis  the  greatest  width  of  the  shell.  The  dimensions  of  a  very  perfect 
specimen  of  aboul  average  size  are:  length  of  pedicle  valve  5.5  mm., 
length  of  brachial  valve  4.9  mm.,  greatest  width  5  mm.,  thickness  3.7 
mm.,  length  of  hinge-line  2  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  from  the  umbonal  region  to  the  postero-lateral  margins  and 
becoming  a  little  incurved  towards  the  beak,  curving  more  gently  to  the 
anterolateral  and  anterior  margins;  mesial  sinus  obsolete;  beak  mod- 
erately incurved,  not  coming  in  contact  with  the  umbo  of  the  opposite 
valve,  perforated  by  a  circular  foramen  which  encroaches  upon  the 
umbonal  portion  id'  the  valve:  cardinal  area  small,  concave,  with  the 
curvature  increasing  towards  the  beak,  the  inferior,  flatter  portion  lying 
nearly  in  the  plane  of  the  valve,  the  lateral  margins  rather  sharply  de- 
fined ;  the  delthyrium  closed  by  the  pseudodeltidium  which  can  scarcely  be 
distinguished  from  the  general  surface  of  the  cardinal  area.  Surface 
of  the  valve  marked  by  about  sixteen  simple,  rounded  plications,  which 
reach  to  the  beak;  they  are  strongest  in  the  middle  of  the  valve  and 
become  fainter  towards  the  cardinal  extremities ;  the  concentric  markings 
faint  or  obsolete. 

Brachial  valve  subcircular  in  outline,  about  equally  convex  with  the 
pedicle,  the  greatest  convexity  posterior  to  the  middle,  the  surface 
curving  from  the  highest  point  rather  abruptly  to  the  cardinal  margin, 
becoming  slightly  compressed  towards  the  cardinal  extremities,  the 
curvature  to  the  antero-lateral  and  anterior  margins  more  gentle ;  on  the 
median  line  the  surface  is  slightly  and  narrowly  depressed  in  the  umbonal 
region,  the  depression  being  nearly  or  quite  obsolete  anterior  to  the 
middle :  the  beak  pointed  and  rather  strongly  incurved.  Surface  marked 
by  plications  entirely  similar  to  those  of  the  opposite  valve  and  alternating 
with  them,  the  median  plication,  however,  does  not  reach  the  beak  but 
originates  in  the  slight  median  depression  of  the  valve  in  the  umbonal 
region ;  concentric  markings  like  those  of  the  opposite  valve. 

Remarks. — Material  for  the  investigation  of  the  internal  characters  of 
this  little  shell  has  not  been  available,  and  consequently  the  generic 
reference  of  the  species  cannot  be  made  with  entire  certainty.  Judging 
from  external  characters  alone,  however,  the  species  has  its  nearest  ally 
in  Hustedia  nwrmoni  of  the  Pennsylvanian  faunas,  the  genotype  of 
Hustedia,  and  because  of  this  the  present  species  is  placed  in  that  genus. 
This  species  is  smaller  than  II.  mormoni,  with  relatively  finer  and  less 
angular  plications,  and  it  is  proportionally  shorter  than  the  average 
specimens  of  that  species. 

Horizon. — Chouteau  limestone. 


NUCLEOSPIRA  453 

Family  MERISTELLID^E 
Genus  NUCLEOSPIRA  Hall 

Description. — Shells  small,  subcircular  in  outline,  the  valves  subequally 
convex,  the  hinge-line  very  short,  the  cardinal  extremities  rounded,  the 
mesial  sinus  of  the  pedicle  valve  and  the  fold  of  the  brachial  valve  low 
and  ill-defined,  usually  obsolete  except  near  the  anterior  margin.  The 
epidermal  layer  usually,  if  not  always,  covered  with  numerous,  closely 
crowded,  fine,  short  spinules.  Pedicle  valve  with  a  very  low  and  small 
cardinal  area  which  is  obscured  in  mature  shells  by  the  incurvature  of 
the  beak,  the  delthyrium  closed  by  a  pseudodeltidium.  Internally  the 
binge-teeth  are  prominent,  approximate,  recurved  at  the  tips  and  sup- 
ported by  thickened  bases  but  not  by  dental  lamelke;  the  muscular  area 
rather  large  and  flabellate,  not  sharply  defined  about  its  margins,  divided 
longitudinally  by  a  low  but  distinct  median  septum  which  extends  nearly 
to  the  front  margin  of  the  valve.  In  the  brachial  valve  the  cardinal 
process  and  hinge-plate  combined  rises  nearly  vertically  from  the  bottom 
of  the  valve,  but  just  above  the  plane  of  the  margins  of  the  valve  it  is 
abruptly  bent  posteriorly  so  that  its  upper  surface  is  nearly  parallel  with 
the  plane  of  the  valve  and  is  extended  beyond  the  margin  of  the  valve 
posteriorly  into  the  umbonal  cavity  of  the  pedicle  valve ;  the  crural  bases 
are  situated  on  the  vertical  face  of  the  plate  at  the  point  of  recurvature, 
the  crura  are  straight  and  slender  with  a  length  equal  to  one-fourth  the 
length  of  the  shell;  the  primary  lamella}  of  the  brachidium  are  greatly 
incurved,  the  spires  are  made  up  of  from  six  to  ten  volutions,  their  apices 
directed  transversely ;  the  jugum  originates  at  about  one-fourth  the  length 
of  the  lamella?,  it  is  inclined  slightly  backward,  the  lateral  branches  are 
united  and  produced  into  a  straight,  elongate,  undivided  stem.  The 
muscular  scars  are  narrow  and  elongate,  ill-defined  and  are  divided  by  a 
median  septum  similar  to  that  of  the  pedicle  valve. 

Remarks.— The  members  of  this  genus  are  usually  easy  to  recognize 
from  their  external  form,  viz,  the  subcircular  and  nearly  equally  convex 
non-plicated  valves.  In  internal  casts  they  may  be  easily  recognized  by 
the  form  of  the  shell  and  by  the  presence  of  the  elongate  median  septum 
in  the  condition  of  a  median  slit,  extending  nearly  to  the  front  of  each 
valve.  The  minute  surface  spines  of  members  of  the  genus  are  com- 
monly destroyed  in  the  fossil  specimens,  but  their  former  presence  often 
may  be  determined  by  the  presence  of  the  minute  papilke-like  bases  of 
the  spines. 


154  .MlSSISSlI'l'lAN    BRACHIOPODA 

\i  CLEOSPJB  \  kowi.kvi  n.  sp. 

Plate  DXXXII,  Pigs.  43-4S 

1001.     Nucleospira  barrisi  Rowley,  Am.  Ucol.,  vol.  27,  p.  350,  pi.  28,  figs. 

Ii;  48.     (Not  N.  barrisi  White). 
1008.     Nucleospira  barrisi  Elowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 

Ber.,  p.  85,  pi.  18,  dgs.  25-27. 

Description. — Shell  small,  lenticular,  usually  a  little  wider  than  long, 
subcircular  or  transversely  subelllptical  in  outline,  the  greatest  width 
near  the  mid-length  of  the  shell,  the  hinge-line  much  shorter  than  the 
greatesl  width,  the  cardinal  extremities  rounded.  The  dimensions  of  a 
nearly  perfect  example  arc:  length  of  pedicle  valve  4.5  mm.,  length 
of  brachial  valve  4.1  mm.,  greatest  width  5  mm.,  thickness  3  mm.,  length 
of  hinge-line  2.3  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  cardinal  margin,  and  more  gently  to  the  lateral  and  an- 
terior margins;  mesial  sinus  originating  in  the  umbonal  region  near  the 
beak,  vvvy  shallow,  rather  broad,  not  sharply  defined  at  any  point  but 
becoming  more  ill-defined  anteriorly;  beak  short  and  obtuse,  but  slightly 
incurved;  cardinal  area  small,  concave,  the  lateral  margins  defined  by  a 
slight  angularity  of  the  surface  separating  the  surface  of  the  lateral  slopes 
of  the  valve  from  that  of  the  cardinal  area.  Surface  of  the  valve  appar- 
ently smooth  or  marked  only  by  obscure  concentric  lines  of  growth,  in 
most  individuals,  but  in  the  best  preserved  examples  the  presence  of  nu- 
merous, minute,  crowded,  appressed  spines  is  shown. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  greatest  convex- 
ity near  or  a  little  posterior  to  the  middle,  the  surface  curving  a  little 
more  abruptly  to  the  posterior  than  to  the  lateral  and  anterior  margins-. 
mesial  portion  of  the  valve  depressed  in  a  narrow  and  shallow  sinus  in 
the  umbonal  region  which  merges  anteriorly  into  a  rather  broad,  ill- 
defined,  flattened  band,  scarcely  or  not  at  all  depressed  below  the  general 
surface,  and  continuing  to  the  front  margin;  beak  obtuse  and  only  slight- 
ly incurved,  the  umbonal  region  scarcely  protuberant  beyond  the  cardinal 
margin  posteriorly.  Surface  of  the  valve  apparently  smooth  or  marked 
only  by  obscure  concentric  lines  of  growth. 

Remarks. — This  little  shell  has  sometimes  been  incorrectly  identified 
as  N.  barrisi,  but  besides  occurring  in  a  very  different  horizon  than  that 
species,  it  is  a  much  smaller  shell.  The  largest  example  of  the  species  ob- 
served by  the  writer  is  under  7  mm.  in  width,  and  in  this  specimen  the 
width  has  been  increased  by  distortion. 

Horizon. — Louisiana  limestone. 


NUCLEOSPIRA  455 

Nucleospira  barrisi  White 
Plate  LXXXII,  Figs.  27-38 

1860.     Nucleospira  barrisi  White,  Jour.  Boston  Soe.  Nat.  Hist.,  vol.  7,  p. 

227. 
1901.     Nucleospira  barrisi  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11,  p. 

199,  pi.  20,  fiys.  7-11. 

Description. — Shell  small,  wider  than  long,  the  greatest  width  near  the 
mid-length,  transversely  subelliptieal  in  outline,  the  hinge-line  very 
short,  the  cardinal  extremities  rounded.  The  dimensions  of  a  complete 
pedicle  valve,  one  of  the  co-types,  are :  length  9  mm.,  greatest  width  10.6 
mm.,  convexity  2.2  mm.  The  dimensions  of  a  brachial  valve,  also  one 
of  the  co-types,  are :  length  8.7  mm.,  greatest  width  11.2  mm.,  convexity 
3.1  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  near  or  poste- 
rior to  the  middle,  the  surface  sloping  with  a  gently  convex  curvature  to 
the  lateral  and  anterior  margins  and  curving  somewhat  more  abruptly 
to  the  cardinal  margin  on  either  side  of  the  beak;  mesial  sinus  originat- 
ing in  the  posterior  half  of  the  valve,  sometimes  nearly  at  the  beak,  nar- 
row and  shallow  but  often  becoming  deeper  and  broader  near  the  front 
margin  and  a  little  produced  in  a  short,  rounded  extension ;  beak  small, 
only  a  little  produced  beyond  the  cardinal  margin  and  only  moderately 
incurved;  cardinal  area  wanting,  the  delthyrium  rather  large,  nearly 
filled  by  the  beak  of  the  opposite  valve,  the  pseudodeltidium;  inconspicu- 
ous, deeply  concave  and  limited  to  the  apical  portion  of  the  delthyrium. 
Internally  the  diductor  muscular  scars  are  large  and  flabellate,  but  are 
scarcely  differentiated  at  their  margins,  the  addiictor  scars  are  much 
smaller  and  in  mature  shells  form  a  narrow,  elongate  depression  in  the 
inner  surface  of  the  valve ;  a  low,  narrow,  mesial  septum  originates  near 
the  apical  portion  of  the  valve,  in  the  midst  of  the  adductor  scar,  and 
continues  nearly  to  the  front  margin. 

Brachial  valve  subequally  or  a  little  more  convex  than  the  pedicle,  the 
greatest  convexity  near  the  middle,  the  surface  curving  more  abruptly  to 
the  cardinal  margin  and  gently  to  the  lateral  and  antero-lateral  margins; 
the  mesial  fold  originating  near  the  middle  of  the  valve,  appearing 
broader  than  the  sinus  of  the  pedicle  valve,  somewhat  abruptly  elevated 
in  front  in  mature  shells  to  accommodate  the  anterior  mesial  extension 
of  the  pedicle  valve,  sometimes  with  a  very  slight,  line-like,  mesial  depres- 
sion for  a  short  distance  back  from  the  anterior  margin  in  full  grown 
examples.  Internally  the  cardinal  process  is  prominent,  and  is  curved  over 
the  margin  of  the  valve  and  projects  posteriorly  beyond  the  margin, 
nearly  filling  the  umbonal  cavity  of  the  pedicle  valve  wiien  the  two  valves 
are  in  articulation,  the  surface  of  the  process  directed  towards  the  um- 
bonal region  of  the  opposite  valve  bears  a  pit-like  excavation  and  its  pos- 


456  Mississiri-iAN   BBACHIOPODA 

terior  margin  is  pounded;  the  muscular  sens  are  more  or  less  ill-defined; 
a  low,  narrow,  mesial  septum  similar  to  that  of  the  pedicle  valve  origin- 
ates a  little  in  I'ronl  of  the  base  of  the  cardinal  process  and  continues  to 
the  middle  or  beyond  the  middle  of  the  valve. 

Surface  of  both  valves  marked  only  by  concentric  lines  of  growth  which 
are  commonly  restricted  to  the  anterior  hall'  of  the  shell  and  often  occur 
only  close  to  the  anterior  margin.  The  delicate  surface  spines  of  the 
genus  have  not,  been  observed  in  any  of  the  specimens  studied,  possibly 
because  of  the  condition  of  preservation. 

Remarks. — This  species  is  characterized  by  the  development  of  a 
stronger  mesial  fold  and  sinus  near  the  front  of  the  shell  than  is  usual  in 
members  of  the  genus.  This  character,  with  the  not  infrequent  develop- 
ment of  rather  strong  concentric  lines  of  growth  towards  the  front,  sug- 
gests a  small  species  of  Alhyris,  but  the  internal  characters,  the  cardinal 
process  of  the  brachial  valve,  and  the  low,  elongate,  median  septum  in  each 
valve  show  at  once  that  its  relationships  are  with  the  genus  Nucleospira. 
The  species  is  also  much  the  largest  one  which  has  been  recognized  in  any 
of  our  Mississippian  faunas.  The  little  shell  from  the  Louisiana  limestone 
which  has  sometimes  been  identified  as  N.  barrisi  is  an  entirely  distinct 
species  and  is  described  in  this  report  as  N.  roivleyi. 

Horizon. — Upper  Kinderhook. 

Nucleospira  minima  Weller 
Plate  LXXXII,  Figs.  49-60 

1906.     Nucleospira  minima  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  16,  p. 
447,  pi.  6,  figs.  29-30. 

Description. — Shell  very  small,  subcircular  in  outline,  lenticular,  the 
two  valves  subequally  convex.  The  dimensions  of  a  large  pedicle  valve 
are:  length  5  mm.,  width  6.1  mm.,  convexity  1.6  mm. 

Pedicle  valve  with  its  greatest  convexity  posterior  to  the  middle,  the 
surface  curving  more  abruptly  to  the  cardinal  margin  and  gently  to  the 
lateral  and  anterior  margins,  not  compressed  towards  the  cardinal  ex- 
tremities ;  the  beak  short  and  obtuse,  incurved,  projecting  but  slightly 
beyond  the  cardinal  margin;  mesial  sinus  originating  at  the  beak,  narrow 
and  groove-like ;  internally  a  faint  median  septum  is  present  in  the  rostral 
portion  of  the  shell  and  extends  anteriorly  to  about  the  middle  of  the 
valve. 

Brachial  valve  similar  to  the  pedicle,  its  greatest  depth  posterior  to  the 
middle,  the  surface  not  compressed  towards  the  cardinal  extremities;  the 
mesial  portion  of  the  valve  narrowly  flattened  on  the  umbo  and  sometimes 
slightly  depressed  as  a  narrow  median  sinus  anteriorly.  Internally  a  low 
and  narrow  median  septum  continues  from  the  beak  nearly  to  the  ante- 
rior margin. 


NUCLEOSPIRA  457 

Surface  of  both  valves  marked  by  fine,  concentric  lines  of  growth. 

Remarks.— This  species  is  much  smaller  than  N.  barrisi  and  does  not  pos- 
sess the  rather  deep  mesial  sinus  which  is  commonly  developed  towards 
the  anterior  margin  in  that  species.  It  is  larger  and  more  nearly  circular 
than  N.  rouieyi. 

Horizon. — Glen  Park  limestone  of  the  Kinderhook. 

Nucleospira  obesa  Rowley 

Plate  LXXXII,  Figs.  39-42 

1900.  Nucleospira  obcsa  Rowley,  Am.  Geol.,  vol.  25,  p.  263.  pi.  5.  figs. 
38-40. 

Description. — Shell  small,  lenticular,  subcircular  in  outline,  usually 
slightly  longer  than  wide,  the  anterior  margin  slightly  truncated,  the 
greatest  width  near  the  mid-length  of  the  shell,  the  hinge-line  much 
shorter  than  the  greatest  width,  the  cardinal  extremities  rounded.  The 
dimensions  of  a  very  perfect  specimen,  a  metatype,  are :  length  of  pedicle 
valve  6.3  mm.,  length  of  brachial  valve  5.9  mm.,  greatest  width  6  mm., 
thickness  4  mm.,  length  of  hinge-line  2.6  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  from  the  umbonal  region  to  the  cardinal  margin  on  each  side  of 
the  beak,  curving  more  gently  to  the  lateral  and  anterior  margins;  mesial 
sinus  obscure,  originating  at  or  near  the  beak  as  a  slight  flattening  of  the 
valve,  becoming  slightly  depressed  in  the  umbonal  region  and  continuing 
to  the  anterior  margin  as  a  narrow  and  shallow  depression  with  very 
gradual  increase  in  width  and  nowhere  sharply  defined ;  beak  short  and 
small,  sharply  pointed  and  moderately  incurved ;  cardinal  area  small, 
concave,  sloping  posteriorly  at  an  angle  of  about  45  degrees  to  the  plane 
of  the  valve,  the  lateral  margins  well  defined.  Internal  characters  not 
observed. 

Brachial  valve  nearly  equally  convex  with  the  pedicle,  the  greatest  con- 
vexity posterior  to  the  middle,  the  surface  curving  somewhat  more  ab- 
ruptly to  the  posterior  than  to  the  lateral  and  anterior  margins,  the  um- 
bonal region  rather  prominent  and  slightly  flattened  along  the  median 
line;  near  the  middle  of  the  valve  a  slight  median  sinus  originates  and 
continues  to  the  front  margin,  this  sinus  being  even  fainter  than  that  of 
the  opposite  valve;  the  beak  rather  strongly  incurved  beneath  the  delthy- 
rium  of  the  opposite  valve.     Internal  characters  not  observed. 

Surface  of  both  valves,  in  the  specimens  observed,  nearly  smooth, 
marked  only  by  obscure  concentric  lines  of  growth. 

Remarks. — The  fine  appressed  surface  spines  which  are  commonly  pres- 
ent on  members  of  this  genus  have  not  been  observed  in  this  species,  prob- 
ably because  of  the  condition  of  preservation.  The  species  differs  from 
N.  barrisi  in  its  smaller  size,  more  nearly  circular  shell,  and  in  the  absence 


458  MississilTlAN   BBACHIOPODA 

of  the  mesial  fold  of  the  brachial  valve    It  differs  Eromi  X.  rovAeyi  in  its 
larger  size,  its  thicker  and  more  elongate  shell. 
Horizon. — Lower  Burlington  white  chert. 

Genus  CAMAROPHORELLA   Hall  and  Clarke 

Description,  Shells  small  or  of  medium  size,  subcireular,  subovate  or 
transversely  subelliptical  in  outline,  the  valves  subequally  convex,  a  fold 
and  sinus  present  or  absent  but  never  strongly  developed.  Surface  of 
the  shell  nearly  smooth,  marked  only  by  fine  concentric  lines  of  growth 
and  sometimes  by  very  obscure  radiating  striffi.  The  pedicle  valve  with 
the  beak  moderately  incurved,  perforated  by  a  rather  large,  subcireular 
foramen  which  encroaches  upon  the  umbo,  the  delthyrlum  closed  by 
deltidial  plates.  Internally  the  dental  plates  are  well  developed,  they 
unite  before  reaching  the  floor  of  the  valve  to  form  a  spondylium  which 
is  supported  by  a  median  septum  which  is  as  long  or  longer  than  the 
spondylium  and  reaches  to  about  the  middle  of  the  valve.  In  the  brachial 
valve  there  is  a  strong  median  septum  extending  one-half  the  length 
of  the  valve,  which  supports  the  hinge-plate  posteriorly ;  throughout  the 
length  of  this  septum  there  is  a  transverse  platform  which  originates 
beneath  the  hinge-plate,  and  which  is  penetrated  by  and  attached  to  the 
septum,  at  its  lateral  margins  this  platform  curves  towards  the  floor  of 
the  valve  and  is  attached  to  it,  forming  a  cavity  between  it  and  the 
inner  surface  of  the  valve  which  is  divided  longitudinally  by  the  median 
septum,  to  this  platform  the  adductor  muscles  were  attached.  The  hinge- 
plate  is  deeply  concave;  the  long  and  slightly  curved  crura  are  continua- 
tions of  this  plate,  being  inserted  on  its  sides  near  the  anterior  margin ; 
the  spiral  cones  consist  of  eight  or  ten  volutions  each,  the  primary 
lamella?  being  united  posterior  to  the  middle  of  the  jugum,  which  rests 
upon  the  high  median  septum,  it  is  saddle-sbaped,  somewhat  similar  to  the 
condition  in  Athyris,  but  much  smaller,  the  accessory  lamella?  are  placed  at 
a  sharp  angle  to  each  other,  the  outer  portions  lying  just  without  and 
parallel  to  the  primary  lamella?,  they  recurve  and  are  attached  to  the 
jugum  near  its  base. 

Remarks. — This  genus  was  originally  described  by  Hall  and  Clarke1  as 
a  near  ally  of  Camaroplioria  because  of  the  well-defined  spondylium  in 
the  pedicle  valve  supported  by  a  median  septum,  associated  with  the 
median  septum  in  the  brachial  valve.  It  has  been  shown  by  Hyde,2 
however,  that  these  shells  are  spire-bearing  with  a  braehidium  of  atheroid 
type.  The  platform  developed  in  the  brachial  valve  for  muscular  attach- 
ment simulates  the  cruralium  in  the  same  valve  in  Camarophoria,  but  the 
lateral  margins  of  the  platform  curve  in  the  opposite  direction  from  the 

l  Pal.  N.  Y.,  vol.  8,  pt.  2,  p.  215.     (1894.) 

2Proc.  Boston  Soc.  Nat.  Hist.,  vol.  34,  No.  3,  pp.  35-65(1908). 


CAMAROPHORELLA  459 

margins  of  the  Camarophoria  cruralium,  and  become  attached  to  the  inner 
surface  of  the  valve,  so  forming  the  pair  of  slender  finger-like  cavities 
lying  on  either  side  of  the  median  septum.  In  addition  to  the  presence 
of  a  spondylium  in  the  pedicle  valve,  the  support  of  the  jugum  by  the 
high  median  septum  of  the  brachial  valve  is  a  character  which  has  not 
heretofore  been  recognized  in  the  atheroid  shells.  The  presence  of  a 
spiral  brachidium  has  never  been  observed  in  the  Kinderhook  species 
here  recorded,  but  in  G.  lenticularis  the  characters  of  the  septa  observed 
in  the  internal  casts  are  so  entirely  like  those  of  the  Ohio  shells  in  which 
the  spires  have  been  observed,  that  their  reference  to  the  same  genus 
seems  to  be  well  founded. 

Camarophorella  lenticularis  (White  and  Whitfield) 

Plate  LXXXII,  Figs.  61-63 

1862.     Pentamerus  lenticularis  AVhite  and  Whitfield,  Proc.  Boston  Soc.  Nat. 

Hist.,  vol.  8,  p.  295. 
1865.     Pantamerus  lenticularis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  117. 

1894.  Camarophorella  lenticularis   Hall    and    Clai'ke,    Int.   to   Study  of 

Brack.,  pt.  2.  pi.  45,  figs.  5-6. 

1895.  Camarophorella  lenticularis  Hall  and  Clarke,  Pal.  N.  Y..  vol.  8,  pt.  2, 

pi.  62,  figs.  46-48. 
1901.     Camarophorella  lenticularis  Weller,    Trans   St.   Louis   Acad.    Sci., 

vol.  11.  p.  162.  pi.  14,  figs.  11-13. 
1908.     Camarophorella  lenticularis  Hyde,  Proc.  Boston  Soc.  Nat.  Hist.,  vol. 

34,  p.  57,  pi.  8,  fig.  34. 

Description. — Shell  small,  lenticular,  broadly  ovate,  or  subcircular  in 
outline,  the  width  usually  greater  than  the  length,  the  greatest  width 
near  the  mid-length  of  the  shell.  The  dimensions  of  the  internal  cast  of  a 
pedicle  valve  are:  length  11.2  mm.,  width  13  mm.,  convexity  3.5  mm. 

Ventral  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  curving  gently  from  the  point  of  greatest  con- 
vexity to  the  lateral  and  anterior  margins,  and  somewhat  more  abruptly 
to  the  cardinal  margin ;  sinus  obsolete  or  rarely  very  faintly  developed 
near  the  anterior  margin ;  the  beak  pointed,  scarcely  incurved,  projecting 
beyond  that  of  the  opposite  valve ;  internally  a  strong  median  septum  is 
developed  which  reaches  nearly  half  way  from  the  beak  to  the  anterior 
margin,  and  supported  by  the  septum  is  a  well-developed  spondylium; 
near  the  hinge-line  a  small,  horizontal  plate  is  developed  from  each  side, 
connecting  the  outer  surface  of  that  structure  with  the  inner  surface  of 
the  valve,  on  each  side  of  the  median  septum  on  the  internal  casts,  the 
surface  is  marked  by  radiating  vascidar  sinuses  which  do  not  reach  the 
anterior  margin  of  the  valve. 

Brachial  valve  equally  or  a  little  less  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  surface  curving  gently 


4(H)  MISSISSIPPIAN   BRACHIOPODA 

from  the  point  of  greatest  convexity  to  the  lateral  and  anterior  margins 
ami  more  abruptly  to  the  cardinal  margin;  mesial  fold  obsolete;  the  beak 
only  moderately  incurved  beneath  that  of  the  opposite  valve,  but  not  ex- 
tending as  Ear  posteriorly;  internally  the  valve  bears  a  median  septum 
which  reaches  from  the  beak  anteriorly  to  or  a  little  beyond  the  middle 
of  the  valve,  from  each  side  of  this  septum,  at  approximately  one-half 
its  height,  a  horizontal  plate  is  developed  whose  distal  margins  for  a 
distance  of  one-third  or  less  the  length  of  the  median  septum,  rests 
against  the  inner  surface  of  the  valve,  the  two  plates  together  forming 
an  elevated  platform  for  muscular  attachment,  which  is  excavated  be- 
neath, the  excavation  being  divided  longitudinally  by  the  median  septum. 
In  the  internal  casts  of  the  valve,  as  they  usually  occur,  the  two  finger-like 
easts  of  this  excavation  are  usually  broken  off;  on  each  side  of  the  median 
septum  the  surface  of  the  internal  casts  of  the  brachial  valve  is  often 
marked  by  radiating  vascular  sinuses  similar  to  those  of  the  opposite 
valve  and  not  reaching  the  anterior  margin  of  the  shell. 

The  surface  markings  of  the  shell  are  unknown,  but  the  shell  was 
probably  smooth  or  marked  only  by  concentric  lines  of  growth. 

Remarks, — This  species  is  known  only  in  the  form  of  internal  casts 
from  the  higher,  yellow  sandstone  of  the  Kinderhook  at  Burlington,  Iowa, 
and  is  usually  in  the  condition  of  casts  of  separate  valves.  When  the 
species  was  made  the  type  of  the  genus  Camarophorella  by  Hall  and  Clarke, 
the  shell  was  supposed  to  be  one  of  the  Pentamericke,  but  specimens  of  a 
closely  related  species  from  the  Waverly  at  Sciotoville,  Ohio,  have  re- 
cently been  shown  by  Hyde1  to  be  spire-bearing,  and  to  belong  among 
the  meristelloid  forms.  No  indication  of  spiral  appendages  have  been 
detected  in  the  Burlington  specimens,  but  in  light  of  the  evidence  fur- 
nished by  the  Sciotoville  specimens  there  can  be  no  doubt  but  that  such 
appendages  were  present  in  the  living  shells.  This  Kinderhook  species 
differs  from  the  Sciotoville  form,  C.  mutabilis  Hyde,  in  its  smaller  size  and 
in  the  absence  of  a  median  fold  and  sinus. 

Horizon. — Kinderhook. 

Camarophorella  missouriensis  (Winchell) 

Plate  LXXXII,  Figs.  70-79 

1865.     Spirigera  Missouriensis  Winchell,  Proc.  Acad.  Nat.  Sci.  Phil,  p.  117. 
1908.     Seminula  bucHeyi  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8,  2nd 
ser.,  p.  79,  pi.  17,  figs.  48-53. 

Description. — Shell  below  medium  size,  longer  than  wide  or  wider  than 
long,  subovate  to  subpentagonal  in  outline.  The  dimensions  of  the  holo- 
type  are :  length  of  pedicle  valve  16.9  mm.,  length  of  brachial  valve  14.8 

lProc.  Boston  Soc.  Nat.  Hist.,  vol.  34,  pp.  35-65  (1908). 


CAMAROPHORELLA  461 

mm.,  greatest  width  16  mm.,  thickness  10.4  nun.  The  dimensions  of  a 
nietatype  of  Seminula  buckleyi  are:  length  of  pedicle  valve  15  mm.,  length 
of  brachial  valve  13.5  mm.,  greatest  width  15.6  mm.,  thickness  7.9  mm. 

Pedicle  valve  deepest  posterior  to  the  middle,  the  umbo  rather  prom- 
inent, the  surface  curving  abruptly  from  the  umbonal  region  to  the 
postero-lateral  margins  becoming  distinctly  inflected  to  the  cardinal  ex- 
tremities, passing  with  a  more  gently  convex  curvature  to  the  antero- 
lateral and  anterior  margins ;  mesial  sinus  originating  at  the  beak  where  it 
is  narrow  and  shallow,  growing  distinctly  broader  and  deeper  towards 
the  front,  roixnded  in  the  bottom,  its  sides  curving  regularly  into  the  lat- 
eral slopes  of  the  valve ;  the  beak  prominent  and  rather  strongly  incurved, 
perforated  by  a  foramen  of  moderate  size  which  encroaches  upon  the  um- 
bonal region,  the  delthyrium  closed  by  a  pseudodeltidium  above  and  by 
the  beak  of  the  opposite  valve  below.  Internally  a  strong  median  septum 
extends  anteriorly  from  the  beak  for  nearly  one-half  the  length  of  the 
valve,  the  dental  lamella*  not  clearly  distinguished  in  any  specimen  ob- 
served but  probably  joined  to  form  a  spondylium  supported  by  the  median 
septum. 

Brachial  valve  about  equally  convex  with  the  pedicle,  its  greatest  depth 
posterior  to  the  middle,  the  surface  sloping  with  a  gently  convex  curva- 
ture to  the  antero-lateral  and  anterior  margins,  curving  somewhat  more 
abruptly  to  the  postero-lateral  margins,  the  beak  strongly  incurved  and 
passing  beneath  the  margin  of  the  pseudodeltidium  of  the  opposite  valve: 
a  narrow,  shallow,  rounded,  median  sinus  similar  to,  but  somewhat  smaller 
than  that  of  the  opposite  valve,  originates  at  the  beak  and  passes  to  about 
the  middle  of  the  mature  valve,  where  it  gradually  becomes  obsolete, 
mesial  fold  obsolete  or  slightly  developed  near  the  front  margin  in  ma- 
ture shells  where  it  is  scarcely  differentiated  from  the  general  curvature 
of  the  surface.  Internally  a  strong  median  septum  is  present,  extending 
from  the  beak  to  about  the  middle  of  the  valve,  the  remaining  internal 
features  not  observed. 

Surface  of  both  valves  marked  by  concentric  lines  of  growth  which  are 
variable  in  strength  and  distribution. 

Bemarks. — Only  three  examples  of  this  rare  species  have  come  under 
the  observation  of  the  writer,  the  largest  being  Winchell's  holotype  of  the 
species.  The  other  two  examples  are  from  the  collection  of  Prof.  R.  R. 
Rowley,  a  cotype  and  a  nietatype  of  his  Seminula  buckleyi.  The  internal 
features  of  the  shell,  so  far  as  they  are  known,  are  shown  only  in  the 
larger  of  the  two  specimens  from  the  Rowley  collection.  This  specimen  is 
exfoliated  sufficiently  to  clearly  show  the  strong  median  septum  in  each 
valve  as  a  dark  line  passing  anteriorly  from  the  beak.  The  presence  of 
these  median  septa  exclude  the  species  from  the  group  of  athyroid  shells 
where  it  has  usually  been  thought  to  belong,  but  without  further  knowl- 


4(>L)  MISSISSIPPIAN    BRACHIOPODA 

edge  of  the  internal  characters,  which  in  lliis  case  can  only  be  gained  by 
sectioning  (lie  specimens,  the  true  relationships  of  the  species  cannot  be 
certainly  determined.  So  far  as  can  be  determined,  considering  both  the 
external  form  and  the  internal  structures,  the  species  seems  to  be  most 
closely  allied  to  the  meristoid1  genus  Camarophorella,  where  it  is  here  placed, 
but  further  knowledge  of  the  shells  may  show  that  the  species  should  be 
considered  as  the  type  of  a  new  genus.  The  external  feature  of  the  shell 
which  seems  to  be  especially  characteristic,  is  the  presence  of  a  faint 
median  sinus  of  the  brachial  valve  which  does  not  continue  to  the  front 
margin  in  mature  examples.  The  general  outline  of  the  shell  seems  to  be 
rather  variable,  judging  from  the  three  examples  studied.  Of  the  pre- 
viously known  species  of  Camarophorella  this  species  most  closely  re- 
sembles C.  mutabilis  Hyde.1  The  general  contour  of  the  two  species  is  essen- 
tially the  same,  including  the  faint  median  sinus  in  the  posterior  portion 
of  the  brachial  valve,  but  C.  missouriensis  differs  from  C.  mutabilis  in  the 
entire  absence  of  the  faint  radiating  stria1  of  that  species. 
Horizon. — Louisiana  limestone. 

Genus  ROWLEYELLA  Weller 

Description. — Shells  small,  subovate  in  outline,  with  subequally  convex 
valves,  fold  and  sinus  wanting,  the  surface  of  the  shell  marked  only  by 
inconspicuous  concentric  lines  of  growth.  Pedicle  valve  with  the  beak 
moderately  incurved  and  perforated  at  its  apex  by  a  subcircular  foramen 
which  encroaches  wholly  upon  the  umbonal  region,  in  contact  with  the 
delthyrium  only  at  its  apex,  the  delthyrium  closed  by  deltidial  plates. 
Internally  a  strong  median  septum  is  present  which  reaches  about  one- 
third  the  length  of  the  valve,  it  supports  a  spondylium  formed  by  the 
union  of  the  dental  plates.  In  the  brachial  valve  is  a  strong  median  sep- 
tum which  reaches  anteriorly  for  one-third  or  more  of  the  length  of  the 
valve,  its  connection  with  the  hinge-plate  and  brachidium  has  not  been 
determined  and  if  a  platform  beneath  the  hinge-plate,  such  as  occurs  in 
Camarophorella  is  present,  its  outer  margins  do  not  join  the  inner  surface 
of  the  valve  to  form  the  pair  of  finger-like  cavities  which  are  present  in 
that  genus ;  the  attachment  of  the  brachidium  to  the  crura  and  the  form 
of  the  jugum  unknown,  the  spiral  cones  are  directed  laterally  and  consist 
of  about  four  volutions. 

Remarks. — The  terebratuliform  contour  of  the  shell  of  the  single  mem- 
ber of  this  genus,  strongly  suggests  its  being  a  loop-bearing  brachiopod, 
and  the  genotype  was  originally  described  as  a  Terebratula.  At  the  time 
the  generic  name  Roivleyella  was  proposed  for  this  species  the  presence  of 
a  spiral  brachidium  had  not  been  detected,  and  while  it  was  recognized 
that  the  presence  of    a   median   septum   in  the  pedicle  valve  was  an  un- 

i  Proc.  Boston  Soc.  Nat.  Hist.,  vol.  34,  No.  3,  p.  56  (1908). 


ROWLEYELLA  463 

known  character  among  the  terebratuloid  shells,  it  was  placed  among 
them  tentatively.  When  the  specimens  were  set  up  for  photographing, 
on  bits  of  modeling  clay,  and  allowed  to  remain  for  several  days,  the  oil 
from  the  clay  was  absorbed  by  the  specimens  in  such  a  manner  as  to  bring 
out  clearly  the  presence  of  a  perfectly  preserved  spiral  brachidium  in  one 
of  the  specimens.  The  relationships  of  the  genus  are  clearly  with 
Camarophorella,  the  only  important  differential  character  which  can  be 
pointed  out,  with  our  present  knowledge,  being  the  absence  of  the  plat- 
form for  muscular  attachment  in  the  brachial  valve  with  its  margins  re- 
curved to  the  inner  surface  of  the  valve  to  enclose  the  two  finger-like 
cavities.  If  a  platform  of  this  sort  is  present,  its  margins  are  entirely 
free.  The  attachment  of  the  jugum  to  the  median  septum  of  the  brachial 
valve  is  another  important  character  of  Camarophorella,  but  it  is  impossible 
to  determine  either  the  presence  or  the  absence  of  such  an  attachment  in 
the  specimens  of  Roideyellei  which  aie  available  for  study. 

ROWLEYELLA  FABULITES    (Rowley  ) 

Plate  LXXXII,  Figs.  64-6!) 

1900.     Terebratida  /abilities  Rowley,  Am.  Geol.,  vol.  23,  p.  265,  pi.  5,  figs. 

51-53. 
1911.     h'owleyella  fabulites  Weller,  Jour.  Geol.,  vol.  19,  p.  448. 

Description. — Shell  small,  terebratuliform,  subovate  in  outline,  the 
greatest  width  near  or  in  front  of  the  mid-length,  the  anterior  margin 
rounded.  The  dimensions  of  a  nearly  complete  example,  but  with  most 
of  the  pedicle  valve  exfoliated,  are :  length  of  pedicle  valve  6  mm.,  length 
of  brachial  valve  5.8  mm.,  greatest  width  5  mm.,  thickness  3.6  mm. 

Pedicle  valve  convex,  with  the  greatest  convexity  posterior  to  the 
middle,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
postero-lateral  margins  and  slightly  inflected  to  the  cardinal  extremities, 
curving  more  gently  to  the  antero-lateral  and  anterior  margins,  anteriorly 
from  near  the  middle  of  the  valve  the  surface  is  slightly  flattened  in  its 
median  portion,  but  is  not  at  all  depressed  in  a  mesial  sinus ;  the  beak 
is  of  moderate  size,  incurved ;  the  foramen  of  moderate  size,  subcircular 
in  outline  and  wholly  encroaching  upon  the  umbonal  portion  of  the  valve ; 
the  delthyrium  not  entirely  hidden  by  the  incurvature  of  the  beak  and 
apparently  closed  by  a  pseudodeltidium.  Internally  the  dental  plates 
are  well  developed  and  become  joined  before  reaching  the  floor  of  the 
valve  to  form  a  distinct  spondylium  supported  by  a  strong  median 
septum  which  reaches  anteriorly  nearly  to  the  center  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  surface  curving 
somewhat  more  abruptly  to  the  posterior  and  postero-lateral  than  to  the 
anterior  and  antero-lateral  margins;  mesial  portion  scarcely  or  not  at  all 
differentiated  from  the  general  curvature  of  the  valve ;  the  beak  incurved 


Hi  I  MISSISSIPPIAN    BRACHIOPODA 

beneath  the  covering  of  the  delthyrium  of  the  opposite  valve.  Internally 
a  strong  median  septum  extends  anteriorly  from  the  beak  for  about  one- 
third  the  length  of  the  valve. 

Surface  of  both  valves  marked  by  moderately  strong,  somewhat  irregu- 
larly distributed,  eoneent ric  lines  of  growth. 

Remarks. — In  the  original  definition  it  is  stated  that  only  two  examples 
of  this  shell  had  been  found  by  the  author  of  the  species.  These  two 
original  examples,  with  two  additional  ones  in  the  collection  of  Walker 
Museum,  are  all  that  have  come  under  the  observation  of  the  writer.  Of 
Rowley's  two  co-types,  one,  the  figured  one,  has  the  shell  entirely  pre- 
served, but  the  second  example  is  partially  exfoliated  and  distinctly  shows 
the  median  septum  of  the  brachial  valve.  Of  the  two  Walker  Museum 
specimens,  the  larger  and  more  complete  one,  whose  dimensions  are  given 
above,  and  which  has  served  mainly  as  the  basis  of  the  above  description, 
is  partially  exfoliated  so  that  the  median  septum  of  the  pedicle  valve  is 
clearly  exhibited,  and  the  smaller  is  an  internal  cast  throughout,  so  that 
the  mesial  septa  of  both  valves  are  clearly  seen.  Rowley's  figured  type 
has  been  carefully  examined,  and  although  the  shell  itself  is  intact,  the 
presence  of  a  median  septum  in  each  valve  seems  to  be  clearly  indicated. 
The  specimen  here  illustrated  is  somewhat  broader,  proportionally,  than 
the  figured  type. 

Horizon. — Lower  Burlington  limestone  (white  chert). 

Family  ATHYRIDiE 

Genus  ATHYEIS  McCoy 

Description.  —  Shells  usually  of  medium  size  or  larger,  transversely  sub- 
elliptical,  subcircular  or  subovate  in  outline,  the  valves  subequally  con- 
vex, the  median  sinus  of  the  pedicle  valve  and  the  fold  of  brachial  valve 
usually  limited  to  the  anterior  portion  of  the  shell  and  sometimes  obso- 
lete. In  the  pedicle  valve  the  beak  is  usually  incurved  so  as  to  conceal 
the  foramen  and  delthyrium,  deltidial  plates  usually  absent.  Internally 
the  hinge-teeth  are  prominent,  recurved  at  the  tips,  and  are  supported  by 
short  but  rather  stout  dental  lamellae  which  are  not  produced  anteriorly 
about  the  muscular  area;  between  the  dental  lamelke  is  a  deep,  trans- 
versely striated  pedicle  cavity,  and  in  front  of  this  an  ovate  muscular  area 
extending  about  one-half  the  length  of  the  valve ;  the  diductor  scars  are 
flabellate  and  usually  ill-defined  about  the  margins,  and  the  adductors 
occupy  a  narrow  central  area  more  sharply  defined.  In  the  brachial  valve 
the  dental  sockets  are  broad  and  deep,  the  socket  walls  are  connected  by 
a  hinge-plate  which  is  perforated  posteriorly,  close  to  the  beak  of  the 
valve,  by  a  circular  opening,  the  median  portion  of  the  plate  is  flat  or  con- 
cave, the  lateral  margins  are  thickened  and  are  produced  anteriorly  into 


ATHYBIS  465 

the  crura.  The  spiral  cones  of  the  hrachidium  lie  base  to  base  with  the 
apices  directed  laterally,  the  crura  are  long  and  convergent  with  the  pri- 
mary lamellae,  abruptly  recurving  at  their  points  of  origin,  the  jugum  is 
saddle  shaped  in  its  main  portion  and  is  situated  posterior  to  the  middle 
of  the  shell,  the  anterior  extremity  of  the  saddle  may  be  simple  or  divided, 
posteriorly  it  is  narrowed  and  inclined  towards  the  beak  of  the  valve  for 
a  short  distance,  thence  rises  abruptly  towards  the  umbo  of  the  pedicle 
valve,  bifurcates  near  the  extremities  of  the  crura,  each  branch  following 
the  curvature  of  the  primary  lamella,  so  forming  accessory  lamellae  which 
lie  between  the  primary  lamella?  and  the  first  band  of  the  secondary 
lamellae.  The  surface  of  the  valves  is  marked  by  broad,  lamellar  expan- 
sions of  the  shell  at  each  growth  line. 

Remarks. — All  the  atheroid  shells  are  characterized  by  a  hinge-plate 
with  an  apical  perforation,  and  in  the  internal  casts  of  the  shells,  the  fill- 
ing of  the  cavity  beneath  the  hinge-plate,  running  up  as  a  finger-like 
point  to  the  perforation  and  directed  towards  the  beak  of  the  opposite 
valve,  is  a  very  conspicuous  feature  of  the  brachial  valve.  The  several 
generic  groups  of  these  species  are  differentiated  largely  by  the  general 
outline  of  the  shell,  and  especially  by  the  nature  of  the  surface  markings. 
In  Athyris  proper  the  lamellar  extensions  of  the  shell  are  highly  charac- 
teristic. 

Athyris  lamellosa    (Leveille) 
Plate  LXXVIII,  Figs.  1-5 ;  15-20 

1835.     Spirifer  lamellosus  Leveille,  Mem.  Soc.  Geol.  de  France,  1st  ser.. 

vol.  2,  p.  39,  figs.  21-23. 
1875.     Athyris    lamellosa  ?  Meek,  Pal.  Ohio,  vol.  2,  p.  283,  pi.  11,  figs 

6a-b. 
1888.     Athyris  lamellosa  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  3,  p. 

49,  pi.  2,  fig.  7. 
1888.     Athyris  ashlandensis  Herrick,  Bull.  Sci.  Lab.  Denison  Univ.,  vol.  4, 

p.  24,  pi.  3,  fig.  6. 

1894.  Athyris  incrassatus  Keyes,  Mo.  Geol.  Snrv..  vol.  5,  p.  91,  pi.  41, 

fig.  10. 

1895.  Athyris  ashlandensis  Herrick.  Geol.  Surv.  Ohio,  vol.  7,  pi.  23,  fig. 

10. 
1895.     Athyris  lamellosa  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  46, 

figs.  16-20. 
1899.     Athyris  lamcUosa  "Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  9,  p.  21, 

pi.  4,  fig.  8. 
1899.     Athyris  lamellosa  Girty,  Mon.  U.  S.  Geol.  Survey,  vol.  32,  p.  561, 

pi.  71,  fig.  7a. 
1904.     Athyris  lamellosa  Girty,  Prof.  Paper  U.  S.  Geol.  Survey,  No.  21, 

p.  49,  pi.  10.  figs.  12-13. 
1909.     Athyris  lamellosa  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  312,  pi. 

14,  figs.  5-6. 


4lili  Mississii'i'iA.N    BRACHIOPODA 

Description. — Shell  of  medium  size  or  larger,  transversely  subelliptical 
in  outline,  the  valves  moderately  convex,  the  length  two-thirds  or  more 
than  two-thirds  the  width,  the  greatest  width  near  or  a  little  posterior  to 
the  mid-length  of  the  shell,  the  hinge-line  much  shorter  than  the  greatest 
width  of  the  shell,  cardinal  extremities  rounded.  The  dimensions  of  a 
latlnr  large  individual  are:  length  39  mm.,  width  51  mm.,  approximate 
thickness  ±24  mm. 

Pedicle  valve  moderately  convex,  the  greatesl  convexity  near  or  poste- 
rior to  the  middle,  the  surface  curving  abruptly  from  the  umbonal  region 
to  the  cardinal  margin  and  gently  to  the  lateral  and  anterior  margins, 
frequently  somewhat  compressed  towards  the  cardinal  extremities;  the 
beak  contiguous  with  that  of  the  opposite  valve,  pierced  by  a  subcircular 
foramen;  cardinal  area  very  narrow  and  inconspicuous,  the  lateral  mar- 
gins usually  well  defined;  delthyrium  broadly  triangular,  the  width  three 
or  four  times  the  height,  nearly  filled  by  the  cardinal  process  and  hinge- 
plate  of  the  brachial  valve  when  the  two  valves  are  in  articulation,  the 
apex  connected  with  the  foramen;  lateral  slopes  convex  except  towards 
the  cardinal  extremities  where  they  sometimes  become  a  little  concave ; 
mesial  sinus  originating  at  or  near  the  beak,  shallow,  rounded  in  the  bot- 
tom, rather  narrow  and  more  or  less  illdefined  laterally,  often  curving 
rather  abruptly  towards  the  opposite  valve  in  adult  specimens  as  it  ap- 
proaches the  anterior  margin. 

Brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  surface  curving  rather 
abruptly  to  the  cardinal  margin  and  more  gently  to  the  antero-lateral 
margins,  sometimes  a  little  compressed  towards  the  cardinal  extremities ; 
the  beak  rather  strongly  incurved  beneath  that  of  the  opposite  valve ; 
mesial  fold  low,  rounded  and  ill-defined  laterally,  sometimes  becoming 
obsolete  towards  the  beak,  often  rather  abruptly  elevated  in  front  in 
adidt  individuals. 

Surface  of  both  valves  marked  by  strong,  subparallel,  concentric,  lam- 
el  liform  extensions  3  to  5  mm.  apart,  towards  the  front  of  the  shell  they 
are  often  much  more  closely  crowded,  and  on  the  body  of  the  shell  weaker 
lamellae  are  often  intercalated  between  the  stronger  ones.  In  all  cases 
where  the  surface  is  well  preserved,  subparallel  lines  of  greater  or  less 
strength  are  disposed  irregularly  between  the  stonger  lamellae. 

Remarks.—  This  species  occurs  not  infrequently  in  such  condition  of 
preservation  that  the  surface  characters  are  more  or  less  obscure,  but  in 
all  cases,  even  in  internal  casts,  the  concentric  lamelhv  are  indicated  by 
the  presence  of  ridges.  In  internal  casts  which  are  frequently  found 
in  the  cherts  of  the  Osage  formations,  the  subovate  muscular  scar  of  the 
pedicle  valve  is  more  or  less  strongly  defined,  dependent  upon  the  age  of 
the  individual,  the  length  of  the  muscular  scar  is  about  equal  to  the  dis- 


ATHYRIS  467 

tance  from  its  anterior  margin  to  the  anterior  margin  of  the  shell,  poste- 
riorly from  the  muscular  sear,  the  east  of  the  transversely  striated  pedicle 
cavity  is  sharply  differentiated,  its  length  heing  about  one-half  that  of 
the  muscular  scar;  the  dental  lamella1,  represented  by  narrow  slits  in  the 
cast,  extend  forward  to  the  anterior  margin  of  the  pedicle  cavity.  In  the 
casts  of  the  brachial  valves  the  cast  of  the  passageway  through  the  pos- 
terior margin  of  the  hinge-plate  to  the  cavity  of  the  shell  is  a  conspicuous 
feature,  being  represented  as  a  median,  finger-like  process  extending  to- 
wards the  beak  of  the  opposite  valve  in  a  direction  nearly  at  right  angles 
to  the  plane  between  the  two  valves. 

The  species  is  a  common  and  only  moderately  variable  one.  The  differ- 
ent appearance  of  the  concentric  markings  of  the  shell  is  frequently  due 
to  differences  in  condition  of  preservation,  but  they  also  vary  to  some  ex- 
tent in  their  distance  apart.  Different  examples  exhibit  some  variation 
in  the  proportional  length  and  width,  but  they  are  frequently  crushed  so 
as  to  make  accurate  measurement  impracticable. 

Horizon. — Upper  Kinderhook,  Burlington  limestone  and  Keokuk  lime- 
stone. 

Athyris  hannibalensis   (Swallow) 

Plate  LXXVIII,  Figs.  10-14 

1860.     Spirigera  Hannibalensis  Swallow,  Trans,  St.  Louis  Acad.  Sci.,  vol.  1, 

p.  649. 
1865.     Spirigera  Hannibalensis  Winehell,  Proc  Acad.  Nat.  Sci.  Phil.,  p.  118. 

1894.  Athyris  hannibalensis  Keves,  Mo.  Geol.  Surv..  vol.  5,  p.  91,  pi.  41, 

%.  9. 

1895.  Athyris  Hannibalensis  Hall  and  Clarke,  Pal.  X.  Y.,  vol.  8,  pt.  2, 

pi.  46,  figs.  13-15. 
1908.     Athyris  hannibalensis  Rowley,  Mo.  Bureau  Geol.  and  Mines,  vol.  8, 
ser.  2,  p.  86,  pi.  18,  figs.  28-30. 

Description. — Shell  of  medium  size,  subelliptical  or  approaching  sub- 
circular  in  outline,  the  valves  moderately  and  subequally  convex,  the 
length  usually  about  seven-eighths  of  the  width  when  the  lamellar  ex- 
tensions of  the  shell  are  removed,  the  hinge-line  less  than  one-half  the 
width  of  the  shell,  the  cardinal  extremities  rounded,  the  greatest  width 
near  the  mid-length  of  the  shell.  The  dimensions  of  two  complete  indi- 
viduals of  about  average  size  are :  length  21.5  mm.  and  21  mm.,  width 
25  mm.  and  23.5  mm.,  thickness  13  mm.  and  12.5  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  curving  abruptly  from  the  umbonal  region  to 
the  cardinal  margins,  and  gently  to  the  lateral  and  anterior  margins ; 
the  beak  small  and  contiguous  with  that  of  the  opposite  valve,  pierced  by 
a  subcircular  foramen;  cardinal  area  narrow  and  inconspicuous,  its 
lateral  margins  more  or  less  well  defined ;  the  delthyrium  broadly  triangu- 


HiS  MISSISSIPPI  AN    BRACI110P0DA 

lar,  the  width  three  or  lour  times  the  height,  nearly  filled  with  the 
cardinal  processes  and  the  binge-plate  of  the  opposite  valve  when  the 
two  valves  arc  in  articulation,  the  apex  connecting  with  the  foramen 
which  encroaches  upon  the  beak;  lateral  slopes  convex,  the  convexity 
continuing  to  the  cardinal  extremities  except  rarely  when  the  valve  is 
slightly  compressed  in  that  direction;  mesial  sinus  more  or  less  obscure. 
rather  narrow  and  ill-defined  laterally,  occasionally  essentially  obsolete, 
sometimes  rather  deep,  usually  developed  to  a  moderate  degree,  originat- 
ing at  or  near  the  beak  as  a  mesial  flattening  of  the  valve  and  becoming 
more  depressed  towards  the  front. 

Brachial  valve  a  Little  more  convex  than  the  pedicle,  the  greatest 
convexity  near  or  posterior  to  the  middle,  the  surface  curving  rather 
abruptly  to  the  cardinal  margin  and  more  gently  to  the  anterolateral 
margins;  the  beak  incurved  beneath  that  of  the  opposite  valve;  mesial 
fold  obscure,  as  usually  developed  it  is  a  mesial  flattening  of  the  valve 
slightly  or  not  at  all  elevated  posteriorly,  and  but  little  elevated  an- 
teriorly. 

Surface  of  each  valve  marked  by  more  or  less  irregular,  sub-parallel, 
concentric,  lamelliform  extensions  from  one  to  three  millimeters  apart, 
those  towards  the  front  of  the  shell  becoming  more  crowded.  Between 
these  stronger  markings  much  fainter  concentric  markings  may  some- 
times be  detected. 

Remarks. — This  species  is  a  close  ally  of  A.  lameilosa,  and  should  perhaps 
not  be  considered  as  distinct  from  it.  There  seems  to  be  a  constant 
difference  between  the  two  species,  however,  in  the  smaller  size  of  A. 
hannibalensis  and  in  its  greater  proportional  length,  its  outline  being  much 
more  nearly  subcircular.  The  concentric  lamella?  are  also  usually  closer 
together  in  this  species,  a  feature  which  might  be  expected  from  its 
smaller  size.  The  character  of  the  surface  markings  of  the  shell  are 
essentially  the  same  in  both  forms.  So  far  as  it  has  been  recognized, 
this  species  is  restricted  in  its  distribution  to  the  Kinderhook  faunas. 

Horizon. — Kinderhook. 

Athyris  papilioniformis  McChesney 

Plate  LXXVIIi,  Figs.  6-9 
1860.     Athyris  spiriferoides  McChesney,  Desc.  New  Spec.  Pal.  Foss.,  p.  46. 

(Not  A.  spiriferoides  Eaton,  1831.) 
1865.     Athyris  papilioniformis  McChesney,    111.   New    Spec.    Foss.,   pi.    6, 

figs.  4a-c. 
1868.     Athyris   ?  papilioniformis  McChesney,   Trans.  Chicago  Acad.  Sci., 

vol.  1,  p.  33,  pi.  6,  figs.  la-c. 

Description. — Shell  of  medium  size,  the  valves  moderately  convex, 
wider  than  long,  the  greatest  width  near  the  cardinal  margin,  the  hinge- 
line  nearly  equal  to  the  greatest  width  of  the  shell,  the  cardinal  extremi- 


ATHYEIS  469 

ties  a  little  rounded.  The  dimensions  of  the  type  specimen  are :  length 
17.5  mm.,  width  28  mm.,  length  of  hinge-line  27  mm.,  thickness  12.5  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  margin,  sloping  in  nearly  straight  lines  to  the  cardinal  extremi- 
ties and  curving  gently  to  the  antero-lateral  margins ;  the  beak  contiguous 
with  that  of  the  opposite  valve,  apparently  pierced  by  a  subcircular  fora- 
men ;  cardinal  area  narrow  and  somewhat  ill-defined ;  the  characters  of 
the  delthyrium  not  determinable  iipon  the  type  specimen,  but  it  is  prob- 
ably broadly  triangular  as  in  A.  lamcllosa;  lateral  slopes  of  the  valve 
convex;  mesial  sinus  deep  and  sub-angular  in  the  bottom,  originating 
at  the  beak,  rather  sharply  defined  laterally. 

Brachial  valve  about  equally  convex  with  the  pedicle,  the  greatest  con- 
vexity near  the  middle,  the  surface  curving  gently  to  the  cardinal  margin 
except  for  a  short  distance  on  each  side  of  the  beak  where  it  is  more 
abrupt,  the  curvature  to  the  antero-lateral  margins  is  gentle,  and  the 
surface  is  somewhat  compressed  towards  the  cardinal  extremities ;  the 
beak  incurved  beneath  that  of  the  opposite  valve ;  the  mesial  fold  origin- 
ating at  the  beak,  flattened  on  top  and  becoming  somewhat  abruptly 
elevated  towards  the  front  of  the  shell,  apparently  with  a  longitudinal, 
mesial  depression  anteriorly. 

Surface  of  both  valves  marked  by  concentric  lamella1  from  one  to  two 
millimeters  apai't  on  the  central  portion  of  the  shell,  becoming  more 
conspicuous  and  somewhat  crowded  towards  the  anterior  margin. 

Remarks. — The  description  of  this  species  has  been  made  from  a  very 
perfect  sulphur  cast  of  the  type  specimen.  The  type  itself  has  been  lost 
and  no  other  example  of  the  species  has  been  seen  by  the  writer.  It  differs 
from  A.  lamcllosa  in  its  smaller  size,  its  greater  proportional  width  with 
the  greatest  width  near  the  hinge-line,  its  much  longer  hinge-line  and 
its  much  stronger  fold  and  sinus.  The  concentric  lamella3  of  the  shell 
are  represented  by  their  basal  portions  only,  but  when  perfectly  preserved 
they  doubtless  were  produced  into  lamelliform  extensions  similar  to 
those  on  A.  lamcllosa,  but  much  thinner  and  closer  together. 

Horizon.— Chester  group. 

Athyris  densa  Hall 
Plate  LXXVII,  Figs.  60-69 

1882.  Centronella  crassicardinalis  Whitfield.  Bull.  Am.  Mus.  Nat.  Hist., 

vol.  1,  p.  55,  pi.  6.  figs.  50-52  (not  Athyris  crassicardinalis  White, 
1860). 

1883.  Centronella  crassicardinalis  Hall,  12th  Ann.  Rep.  Geol.  Surv.  Ind., 

pi.  29.  fias.  50-52. 

1894.  Athyris  densa  Hall,  13th  Rep.  N.  Y.  State  fieol.,  p.  651. 

1895.  Athyris  densa  Hall  and  Clarke,  Pal    N.  Y.,  vol.  8,  pt.  2,  p.  364, 

pi.  46,  figs.  6-12 


470  MlssissHTl.W    BBACHIOPODA 

L897.     Athyrisdensa  Hall,  14th  Rep.  N.  V.  State  Geol.,  p.  358,  pi.  9,  figs.  3-9. 
1906.     Centronella  ?  1  crassicardinalis  Beede,  30th  Ann.  Rep.  Geol.  Surv. 

[nd.,  p.  1308,  pi.  2-2.  figs.  .")()-,-)•_'. 
1906.     Athyris  <1<  nsa  Beede,  30th  Ann.  Bep.  Geol.  Surv.  Ind.,  p.  1320,  pi.  19, 

figs.  2-2e. 

Description. — Shell  below  medium  size,  wider  than  long,  the  valves 
much  thickened  posteriorly,  unequally  convex,  the  greatest  width  near 
the  mid-length  of  the  shell,  the  hinge-line  arcuate,  shorter  than  the 
greatest  width,  the  cardinal  extremities  rounded.  The  dimensions  of  a 
complete  specimen,  one  of  the  co-types  of  the  species,  are:  length  18 
mm.,  width  22  mm.,  thickness  11.5  mm. 

Pedicle  valve  shallow,  depressed  in  its  posterior  half,  curving  towards 
the  opposite  valve  anteriorly,  the  surface  nearly  straight,  gently  convex 
or  sometimes  a  little  concave  along  tlie  transverse  line  of  the  valve  be- 
tween the  points  of  greatest  Lateral  extent,  except  near  the  lateral 
margins  where  it  is  abruptly  bent  towards  the  opposite  valve  and  is  even 
inflected  in  the  larger  examples;  the  beak  not  incurved,  contiguous  with 
the  umbo  of  the  opposite  valve,  pierced  by  a  small  sub-semicircular 
foramen  which  is  joined  broadly  with  the  apex  of  the  delthyrium;  the 
false  cardinal  area  sharply  defined  along  its  ventral  margin  or  curving 
very  abruptly  into  the  lateral  slopes  of  the  valve,  rather  broad  and  nearly 
flat,  or  slightly  concave  from  the  cardinal  to  the  ventral  margins,  the 
two  portions  of  the  area  on  opposite  sides  of  the  delthyrium  not  lying 
in  a  plane,  if  produced  to  the  center  of  the  delthyrium  they  would  meet 
in  an  obtuse  angle,  laterally  the  area  continues  on  each  side  with  the 
curvature  of  the  valve  nearly  or  quite  to  the  greatest  transverse  diameter 
of  the  valve ;  delthyrium  broadly  triangular,  wider  than  high,  nearly 
filled  by  the  beak  and  cardinal  processes  of  the  opposite  valve  when  the 
valves  are  in  articulation,  the  apex  connected  with  the  foramen;  lateral 
slopes  depressed,  nearly  straight  transversely,  but  convex  antero-poster- 
iorly ;  mesial  sinus  originating  near  or  at  some  distance  anterior  to  the 
beak,  shallow,  usually  narrow  but  sometimes  broad  and  ill-defined,  pro- 
duced anteriorly  in  adult  individuals. 

Brachial  valve  more  strongly  convex  than  the  pedicle,  the  greatest 
convexity  near  the  middle,  the  surface  sloping  with  a  convex  curvature 
from  the  median  line  to  the  lateral  margins,  the  curvature  somewhat 
more  abrupt  towards  the  cardinal  and  anterior  margins;  the  beak  in- 
curved beneath  that  of  the  opposite  valve ;  mesial  fold  ill-defined  later- 
ally, passing  without  demarcation  into  the  lateral  slopes,  flattened  on  top 
or  sometimes  with  a  median  longitudinal  depression  towards  the  front. 

Surface  of  both  valves  marked  by  fine,  sublamellose,  concentric  lines 
of  growth,  which  are  crowded  at  intervals,  especially  towards  the  front, 
to  form  much  stronger  growth  lines. 


ATHYRIS  471 

Remarks. — This  species  may  be  easily  recognized  by  the  transversely 
flattened  surface  of  the  pedicle  valve,  and  by  the  conspicuous  false 
cardinal  area  of  the  same  valve.  It  was  originally  described  by  Whitfield 
as  Centronella  crassicardinalis,  but  is  clearly  not  a  member  of  that  genus. 
Whitfield's  specific  name  is  preoccupied  in  the  genus  Athyris  by  A. 
crassicardinalis  White,  consequently  the  name  A.  densa  H.  and  C,  must 
be  retained  for  the  species.  Whitfield's  description  was  based  upon  a 
single,  small  pedicle  valve  which  was  proportionally  somewhat  more 
elongate  than  usual,  but  is  clearly  the  same  as  Hall  and  Clarke's 
species. 

Horizon .  —  Salem  limestone. 

Athyris  crassicardinalis  White 
Plate  LXXVII,  Figs.  1-20 

1860.     Athyris  crassicardinalis  White,  Jour.  Boston  Soc.  Nat.  Hist.,  vol.  7, 

p.  229. 
1899.     Cliothyris  crassicardinalis  Girty,  Mon.  U.  S.  Geol.  Survev,  vol.  32, 

p.  567,  pi.  71,  fig.  8a. 
1901.     Athyris  crassicardinalis  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  11, 

p.  186,  pi.  16,  figs.  18-24. 

Description. — Shell  small,  biconvex,  suboval  or  subcircular  in  outline, 
the  width  equal  to  or  greater  than  the  length,  the  greatest  width  near  the 
mid-length  of  the  shell,  the  hinge-line  shorter  than  the  greatest  width,  the 
cardinal  extremities  rounded.  The  dimensions  of  two  pedicle  valves 
are:  length  9  mm.  and  10.3  mm.,  width  10  mm.  and  10.2  mm.,  convexity 
4.5  mm  and  4  mm.  The  dimensions  of  a  brachial  valve  are :  length  8 
mm.,  width  9  mm.,  convexity  3  mm. 

Pedicle  valve  strongly  convex,  the  greatest  convexity  near  or  posterior 
to  the  middle,  most  elevated  along  the  median  line,  the  surface  curving 
abruptly  from  the  umbonal  region  towards  the  cardinal  margin  and 
sloping  laterally  from  the  median  line  with  a  gently  convex  curvature ; 
median  sinus  obsolete,  the  median  portion  of  the  valve  slightly  flattened 
in  an  ill-defined,  narrow  band  from  which  the  surface  slopes  laterally  in 
each  direction ;  beak  small,  pointed,  moderately  incurved ;  cardinal  area 
obsolete ;  delthyrium  large,  open,  broadly  triangular.  Internally  the 
hinge-teeth  are  large  and  strong,  they  are  nearly  horizontal  in  position 
and  are  directed  medially,  growing  out  from  the  inner  surface  of  the 
valve  as  shelf-like  processes  which  are  concave  externally ;  the  muscular 
scars  are  large  but  ill-defined,  sometimes  divided  longitudinally  by  a 
slightly  raised  rib. 

Brachial  valve  much  less  convex  than  the  pedicle  valve,  arched  from 
the  posterior  to  the  anterior  margins,  depressed-convex  transversely  : 
mesial  fold  obsolete,  the  median  portion  of  the  valve  slightly  flattened 
along  a  narrow,  ill-defined  region  from  which  the  surface  slopes  laterally ; 


472  mississii'I'IAN    BRACHIOPODA 

beak  small,  moderately  Incurved,  Internally  the  cardinal  process  is  very 
broad  and  thick,  and  is  coalesced  with  the  socket  plates,  the  hinge 
sockets  being  excavated  from  its  sides,  its  main  surface  lies  nearly 
parallel  In  the  plane  of  the  valve,  is  suberescentic  in  outline,  with  a 
raised  margin  posteriorly  and  laterally,  anteriorly  the  surface  drops 
abruptly  to  the  floor  of  the  valve,  the  lateral  margins  are  extended 
farther  anteriorly  than  the  median  part  and  doubtless  bear  the  crura; 
the  muscular  scars  smaller  and  a  little  more  deeply  excavated  and 
more  sharply  defined  1  hail  those  of  the  opposite  valve,  divided  longitud- 
inally by  a  faint  median  septum. 

Surface  of  both  valves  smooth,  or  nearly  smooth,  marked  only  by 
more  or  less  indistinct,  concentric  lines  of  growth. 

Remarks. — The  generic  relations  of  this  shell  are  uncertain.  Tt  is 
not  a  true  member  of  the  genus  Athyris,  neither  can  it  be  placed  in  another 
genus  with  any  more  certainty.  It  is  not  unlikely  a  representative  of  an 
undescribed  genus,  but  the  character  of  its  brachidium  should  be  known 
before  defining  it  as  new.  For  the  present,  therefore,  it  may  be  allowed 
to  remain  in  Atliyris,  where  it  was  originally  placed  by  the  author  of  the 
species. 

Horizon.— Upper  Kinderhook. 

Genus  CLIOTHYFIDINA  Buckman 

Description. — Shells  small,  of  medium  size  or  large,  from  subcircular 
to  transversely  subelliptical  in  outline,  mesial  sinus  of  the  pedicle  valve 
and  fold  of  the  brachial  valve  well  developed  or  obsolete,  the  surface 
of  the  valves  marked  by  broad,  thin,  lamellar  extensions,  which  are  divided 
neai'ly  or  quite  to  their  bases  into  long,  flat  spines.  The  beak  of  the  pedicle 
valve  usually  incurved  so  as  to  conceal  the  foramen  and  delthyrium  in  the 
mature  shells,  the  dental  lamellae  and  muscular  scars  as  in  Athyris. 
In  the  brachial  valve  the  hinge-plate  and  brachidium  are  similar  to  the 
same  structures  in  Athyris. 

Remarks.— This  generic  group  has  been  called  Cliothyris  by  Hall  and 
Clarke,1  on  King's  authority,  and  authors  have  commonly  used  that  name 
since  the  publication  of  their  work.  It  has  been  shown  by  Buckman,2 
however,  that  the  name  Cliothyris  must  be  accredited  to  Phillips  and  if 
used  at  all  must  be  considered  as  a  synonym  of  Athyris,  over  which  it  has 
priority,  and  be  has  proposed  the  new  generic  name  Cliothyrirlin,i  to 
designate  this  group  of  shells.  The  genus  differs  from  Atliyris.  as  used  in 
this  work,  in  the  form  of  its  surface  markings,  the  concentric  lamellse 
developed  from  the  lines  of  growth  being  divided  into  flat  spines  by 
deep  incisions.     These  fringe-like    lamellse    are    commonly  more  or  less 

iPal.  N.  Y.,  vol.  8,  pt.  2,  p.  90.     (1894.) 

2Ann.  and  Mag.  Nat.  Hist.,  ser.  7,  vol.  18,  p.  321  (1906). 


CLIOTHYRIDINA  473 

completely  removed  from  the  fossil  specimens,  but  usually  some  bases  of 
the  spines  or  more  complete  fragments  of  the  lamellae  can  be  detected 
unless  the  shell  has  been  too  badly  exfoliated.  This  is  the  commoner 
genus  of  the  two  in  our  faunas,  and  the  shells  are  usually  smaller  and 
more  lenticular  than  Athyris,  although  this  statement  is  not  applicable  to 
all  the  species  of  the  genus. 

Cliothyridina  glenparkensis  n.  sp. 

Plate  LXXVIII,  Figs.  21-24 

1909.     Cleiathyris  royssi  Weller,   Bull.    Geol.    Soc.   Am.,    vol.    20,   p.   313, 
pi.  14,  figs.  1-3. 

Description. — Shell  lenticular  in  form,  the  two  valves  nearly  equally 
convex,  transversely  subelliptical  in  outline,  the  length  about  six-sevenths 
of  the  width,  the  greatest  width  near  the  mid-length  of  the  shell,  the 
hinge-line  much  shorter  than  the  greatest  width.  The  dimensions  of  a 
nearly  perfect  individual  are:  length  18  mm.,  width  21  mm.,  thickness 
9.5  mm. 

Pedicle  valve  moderately  convex,  the  greatest  depth  posterior  to  the 
middle,  the  surface  curving  most  abruptly  to  the  cardinal  margin ;  the 
mesial  portion  of  the  valve  slightly  flattened,  and  sometimes  slightly 
depressed  anteriorly  in  a  narrow,  obscure  sinus;  the  beak  small,  pointed, 
in  close  contact  with  the  umbo  of  the  opposite  valve,  pierced  by  a  sub- 
circular  foramen ;  cardinal  area  obsolete,  the  delthyrium  broadly  triangu- 
lar and  filled  by  the  beak  of  the  opposite  valve. 

Brachial  valve  subequally  or  sometimes  slightly  more  convex  than  the 
pedicle,  the  greatest  depth  near  or  a  little  posterior  to  the  middle,  the 
surface  slightly  compressed  towards  the  cardinal  extremities;  the  mesial 
portion  of  the  valve  flattened  along  a  narrow  band  from  the  beak  to  the 
front  margin,  but  not  elevated  into  a  fold,  the  mesial  flattening  of  the 
valve  being  more  conspicuous  than  that  of  the  opposite  valve;  the  beak 
incurved  beneath  that    of    the    opposite  valve  and  filling  the  delthyrium. 

Surface  of  both  valves  marked  by  regular,  fine,  crowded,  concentric, 
imbricating,  lamellose  lines  of  growth,  which,  when  the  surface  characters 
are  perfectly  preserved  are  produced  into  rows  of  closely  imbricating 
fringes  of  flattened  spines. 

Remarks.  —  The  species  Athyris  roissyi  has  been  given  so  broad  an  inter- 
pretation by  Davidson,1  as  to  include  essentially  all  of  the  species  here 
referred  to  the  genus  Cliothyridina,  but  as  used  by  DeKoninck,  the  name 
applies  to  shells  which  are  essentially  like  those  here  described  as  C.  glen- 
parkensis; Leveille's  original  illustrations  of  the  species,  however,  represent 
a  shell  with  a  well-developed  fold  and  sinus  similar  to  the  American  C. 

iBrit.  Foss.  Brach.,  vol.  2,  p.  84,  pi.  18,  figs.  1-11.     (1860.) 


474  MISSISSII'I  IAN     HRACI  ■[(ll'(ll)A 

prouti,  so  thr  name  cannol  be  used  to  designate  the  .shell  under  considera- 
tion. C.  glenparkensis  is  perhaps  most  closely  related  to  C.  hirsuta, 
bul  il  is  Larger  than  that  species  and  is  proportionally  broader  and 
thinner,  with  more  crowded  and  thinner  pectinated  lamelhe.  It  differs 
from  C.  sublamellosa,  which  has  sometimes  been  referred  to  C.  roissyi 
in  being  broader  and  thinner,  and  in  having  the  valves  suhequally 
convex.  In  size  the  species  exhibits  considerable  variation,  some  examples 
attaining  a  Length  of  30  mm.  or  more,  hut  none  of  these  larger  individuals 
have  been  observed  in  an  ondistorted  condition. 
Horizon. — Fern  Glen  formation. 

CuoTiiYHimx  \  prouti  (Swallow) 

Plate  LXXIX,  Figs.  13-16 

1860.     Spirigt  ra  Proutii  Swallow.  Trans.  St.  Louis  Acad.  Sci.,  vol.  1,  p.  649, 
issl.     Spirift  ra  tt  nu  raria  Miller,  Jour.  Cinn.  Soc.  Nat.  Hist.,  vol.  4,  p.  314, 

pl.  7,  figs.  9-9b. 
1894.     A  thy  r  is  proutii  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  91. 
1909.     Clciothyris  prouti  Weller,   Bull.   Geol.   Soc.   Am.,   vol.  20,  p.  314, 

pl.  14,  figs.  12-1."). 

Description. — Shell  transversely  subelliptical  in  outline,  the  greatest 
width  near  the  mid-length  of  the  shell,  the  hinge-line  shorter  than  the 
greatest  width,  the  cardinal  extremities  rounded,  the  fold  and  sinus  con- 
spicuously developed.  The  dimensions  of  two  individuals  are:  length 
17.5  mm.  and  16  mm.,  width  22.5  mm.  and  21.5  mm.,  thickness  15  mm. 
and  11  mm. 

Pedicle  valve  strongly  convex,  most  prominent  posterior  to  the  middle 
the  surface  curving  strongly  from  the  umbonal  region  to  the  margins, 
most  abruptly  to  the  cardinal  margin;  mesial  sinus  large  and  deep, 
originating  near  the  beak  and  becoming  proportionally  more  profound 
anteriorly,  rounded  in  the  bottom,  defined  on  each  side  by  a  rounded 
ridge,  in  mature  individuals  produced  anteriorly  into  a  lingual  extension 
of  greater  or  less  length ;  beak  rather  prominent,  incurved,  in  close  contact 
with  the  umbo  of  the  opposite  valve,  pierced  by  a  circular  foramen ; 
cardinal  area  obsolete  except  in  old  shells  in  which  there  is  a  more  or 
less  conspicuous,  flattened  border  or  false  cardinal  area  along  the  car- 
dinal margin;  delthyrium  broadly  triangular,  nearly  filled  by  the  beak  of 
the  opposite  valve. 

Brachial  valve  strongly  convex,  the  greatest  convexity  near  or  anterior 
to  the  middle,  the  surface  rather  strongly  convex  from  the  cardinal  to 
the  anterior  margin ;  mesial  fold  obscure  or  obsolete  posteriorly,  becoming 
strongly  developed  anteriorly,  especially  in  old  shells,  more  or  less  ill- 
defined  laterally;  the  beak  strongly  incurved,  nearly  filling  the  delthyrium 
of  the  opposite  valve. 


CLIOTHYMDINA  475 

Surface  of  both  valves  marked  by  closely  arranged,  thin,  concentric, 
imbricating  lamella1,  which  ai'e  produced  very  regularly  into  fine,  flat- 
tened spines,  the  spines  of  successive  concentric  rows  being  arranged  in 
radiating  series  so  that  the  entire  surface,  even  when  the  spines  them- 
selves are  in  large  part  destroyed,  presents  the  appearance  of  being 
regularly  and  finely  marked  in  a  reticulate  manner. 

Remarks. — This  species  is  not  closely  allied  to  any  other  American 
member  of  tbe  genus.  Its  nearest  allies  are  found  in  the  European  Athyris 
squawdgera  DeKon.  and  Athyris  roissyi  Leveille. 

Horizon.  —  Chouteau  limestone  and  Fern  Glen  formation. 

Cliothyridina  obmaxima    (McChesney) 
Plate  LXXIX.  Figs.  1-11 

1861.     Athyris  obmaxima  McChesney,  Desc  New  Spec.  Foss.,  p.  80. 
1863.     Spirigera  pectinifera  Swallow.  Trans.  St.  Louis  Acacl.  Sci.,  vol.  2, 

p.  88. 
1874.     Spirigera  obmaxima  White.  Prelim.  Pep.  Inv.  Fo.-s.,  p.  17. 
1877.     Spirigera-  obmaxima  White,  U.  S.  Geol.  Survevs  W.  100th  Mer.,  vol. 

4,  p.  92,  pi.  5,  fig.  12. 
1895.     Athyris  incrassata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt   2,  pi.  83, 

fig.  39.     (Not  pi.  46,  fig.  21.) 
1909.     Cleiothyris  incrassata  Weller,  Bull.  Geol.  Soc.  Am.,  vol.  20,  p.  313, 

pi.  14.  figs.  8-10. 

Description.  —  Shell  large,  transversely  subelliptical  in  outline,  greatest 
width  near  the  mid-length  of  the  shell,  the  hinge-line  much  shorter  than 
the  greatest  width,  the  cardinal  extremities  rounded,  fold  and  sinus 
strongly  developed  towards  the  anterior  margin.  The  dimensions  of  a 
nearly  perfect  individual  are :  length  40  mm.,  width  52  mm.,  thickness 
24  mm.     Some  of  the  largest  examples  have  a  width  of  75  mm.  or  more. 

Pedicle  valve  rather  strongly  convex,  strongly  arched  from  beak  to 
front  along  the  median  line,  the  greatest  prominence  posterior  to  the 
middle,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  margin,  and  much  more  gently  to  the  antero-lateral  margins, 
sometimes  a  little  compressed  towards  the  cardinal  extremities ;  mesial 
sinus  obscure  or  obsolete  at  the  beak,  but  usually  originating  in  or  near 
the  umbonal  region,  rounded  in  the  bottom  and  ill-defined  laterally, 
growing  rapidly  stronger  anteriorly,  often  becoming  profound  near  the 
anterior  margin  and  produced  in  a  lingual  extension  of  greater  or  less 
length;  beak  rather  small  and  pointed,  incurved,  in  contact  with  the 
umbonal  region  of  the  opposite  valve,  pierced  by  a  subcircular,  oblique 
foramen;  cardinal  area  obsolete,  the  delthyrium  broadly  triangular,  con- 
nected at  its  apex  with  the  foramen,  almost  entirely  filled  with  the  beak 
of  the  opposite  valve. 


476  MISSISSIPPIAN    BSACHIOFODA 

Brachial  valve  somewhat  more  convex  than  the  pedicle,  the  greatest 
convexity  towards  the  anterior  margin,  the  surface  strongly  convex  on 
each  side  of  the  fold  and  sinus,  the  curvature  being  most  abrupt  to  the 
cardinal  margin  and  least  to  the  lateral  margins;  mesial  fold  obscure  or 
obsolete  towards  the  beak,  becoming  strongly  elevated  anteriorly,  rounded 
on  top  and  not  sharply  denned  Laterally;  beak  strongly  incurved  and 
filling  the  delthyriuin  of  the  opposite  valve. 

Surface  of  both  valves,  as  usually  preserved  and  when  not  greatly 
exfoliated,  marked  by  crowded,  more  or  less  regular,  thin,  imbricating 
lamellose  lines  of  growth,  which  are  often  somewhat  wavy  along  their 
free  m ; 1 1 •  ii' i 1 1 s .     In  rare  instances  the  concentric  lamellae  are  seen  to  be 

produ I  into  thin,  rather  broad,  lamellae,  which  are  divided  by  grooves 

or  slits  into  ribs  or  spines,  giving  to  the  shell  the  essential  characteristics 
of  the  genus  CUothyridina. 

Remarks. — This  species  has  commonly  been  confused  with  C.  incrassata. 
The  two  forms  are  closely  allied,  but  they  seem  to  be  sufficiently  distinct 
to  warrant  their  recognition  as  separate  species,  although  it  is  probable 
that  some  intermediate  examples  may  he  found.  C.  obmaxima  grows 
to  a  larger  .size  than  C.  incrassata,  sometimes  attaining  a  width  of  75  mm. 
or  more;  it  is  always  broader  than  Ions,  with  a  profound  sinus  which 
originates  nearer  the  beak  than  that  of  C.  incrassata.  The  species  occurs 
most  commonly  in  the  Fern  Glen  formation  and  in  the  Keokuk,  while 
C.  incrassata  has  been  observed  only  in  the  Burlington  limestone.  The 
shell  described  as  Spirigera  pectinifera  by  Swallow,  has  never  been  illus- 
trated, and  the  types  are  lost,  but  the  description  is  a  good  one  and  closely 
applies  to  an  example  of  C.  obmaxima,  upon  which  some  of  the  delicate 
surface  markings  are  preserved,  the  species  is  recorded  from  Keokuk,  Iowa, 
from  which  locality  many  excellent  examples  of  C.  obmaxima  have  been 
secured. 

Among  European  species  the  shell  described  by  Phillips  as  Spirifera 
glabristria,1  is  perhaps  identical  with  our  American  C.  obmaxima.  David- 
son has  included  the  form  in  his  broad  interpretation  of  AtJiyris  roissyi,2 
and  DeKoninck  has  described  a  new  species  under  the  name  Athyris  ingens? 
which  is  a  close  ally.  Phillips'  specific  name  has  priority,  and  if  the 
American  shell  should  be  considered  as  identical  with  the  European,  the  name 
C.  glabristria  Phill.,  would  have  to  take  precedence  over  C.  obmaxima 
McChesney. 

Horizon.— Upper  Kinderhook,  Burlington  limestone  and  Keokuk  lime- 
stone. 

iGeol.  Yorks.,  vol.  2,  p.  220,  pi.  10,  fig.  19  (1836). 

2  Brit.  Foss.  Brach.,  vol.  2,  p.  84,  pi.  18,  figs.  1-4  (1860). 

3  Faun,  du  Calc.  Carb.  de  la  Belg.,  pt.  6.  p.  85,  pi.  20,  figs.  1-10.  (1887.) 


CLIOTHYRIMNA  ill 

Cliothyridina  incrassata  (Hall) 
Plate  LXXIX,  Fig.  12 

1858.     Athyris  incrassatus  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  600,  pi.  12, 

fig-  6. 
1895.     Athyris  incrassata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  46. 

fig.  21.     (Not  pi.  83,  fig.  39.) 
1899.     Athyris  incrassata   (?)    Girtv,  Mon.  U.   S.   Geol.   Survey,  vol.  32, 

p.  562. 

Description. — Shell  above  medium  size,  subovate  in  outline,  the  length 
and  width  subequal,  or  longer  than  wide,  the  greatest  width  near  the 
mid-length ;  the  hinge-line  much  shorter  than  the  greatest  width,  the 
cardinal  extremities  rounded ;  fold  and  sinus  strongly  developed  an- 
teriorly. The  dimensions  of  a  nearly  complete  pedicle  valve  are :  length 
±42.5  mm.,  width  40  mm.,  convexity  10  mm.  The  dimensions  of  a 
brachial  valve  are :  length  40  mm.,  width  45  mm.,  convexity  15  mm. 

Pedicle  valve  moderately  convex,  arched  from  the  beak  to  the  front 
margin  along  the  median  line,  greatest  depth  near  the  middle,  the  surface 
curving  rather  abruptly  from  the  umbonal  region  to  the  cardinal  margin, 
much  more  gently  to  the  antero-lateral  margins,  often  somewhat  com- 
pressed towards  the  cardinal  extremities;  mesial  sinus  obscure  or  obsolete 
posteriorly,  usually  originating  near  the  mid-length  of  the  valve,  rounded 
in  the  bottom  and  ill-defined  laterally,  becoming  deep  at  the  anterior 
margin ;  beak  rather  small  and  pointed,  incurved,  pierced  by  a  sub- 
circular  foramen;  cardinal  area  obsolete,  the  delthyrium  broadly  tri- 
angular. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
near  the  middle,  the  surface  strongly  convex  on  each  side  of  the  fold 
and  sinus,  the  curvature  most  abrupt  to  the  cardinal  margin ;  mesial  fold 
obsolete  or  nearly  obsolete  posterior  to  the  middle,  becoming  strongly 
elevated  anteriorly,  rounded  on  top,  not  sharply  defined  laterally;  beak 
strongly  incurved. 

In  the  usual  condition  of  preservation,  the  surface  of  both  valves  is 
marked  by  more  or  less  crowded,  concentric  lines  of  growth.  When  not 
exfoliated  these  growth  lines  are  produced  into  lamella1  which  are  divided 
by  grooves  or  slits  into  fine  ribs  or  spines. 

Remarks.— C.  incrassata  is  a  close  ally  of  C.  obmaxima,  being  distinguished 
from  that  species  by  its  less  transverse  form,  and  by  the  more  anterior 
position  of  the  point  of  origin  of  the  fold  and  sinus.  It  occurs  commonly 
in  the  Burlington  limestone,  where  the  allied  species  is  rarely  found, 
and  has  not  been  observed  in  the  Fern  Glen  or  the  Keokuk  where  C. 
obmaxima  is  most  abundant.  Not  infrequently  examples  of  this  species 
are   dark  colored,   sometimes   almost   black,   especially   in   the   umbonal 


478  M  ISSISSIl'I'IAN     HU.U'IllOl'ODA 

portion  of  the  pedicle  valve.    This  coloration  in  the  fossil  shell  is  perhaps 
duo  to  some  original  coloration  in  the  living  shell. 
Horizon. — Burlington  limestone. 

CUOTHVRIDINA  TENUILINEATA   (Rowley) 

Plate  LXXX,  Pigs.  1-12 

1900.  Athyris  tenuilineata  Rowley,  Am.  Geol.,  vol.  25,  p.  264,  pi.  5,  figs. 

31-33. 

1901.  Cleiothyris  hirsuta  Weller,  Trans.  St.  Louis  Acad.  Sei.,  vol.  11,  p. 

187,  pi.  Hi.  figs.  25-27. 

Description.-  Shell  small,  lenticular,  subcircular  in  outline,  the  length 
and  breadth  subequal,  the  greatest  width  near  the  mid  length  of  the  shell, 
the  hinge-line  much  shorter  than  the  greatest  width,  the  cardinal  ex- 
tremities rounded.  The  dimensions  of  two  nearly  perfect  examples, 
metatypes,  are:  length  of  pedicle  valve  8.9  mm.  and  8  mm.,  length  of 
brachial  valve  8.1  mm.  and  7.5  mm.,  greatest  width  8.7  mm.  and  8.7 
mm.,  thickness  5.1  mm.  and  4.8  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  cardinal  margin  on  each  side  of  the  beak,  and  more  gently 
to  the  lateral  and  anterior  margins;  mesial  portion  of  the  valve  slightly 
flattened  anteriorly  but  not  depressed  to  form  a  mesial  sinus;  the  beak 
rather  small,  sharply  pointed  and  incurved,  perforated  by  a  subcircular 
foramen  which  encroaches  upon  the  umbonal  region  of  the  valve ;  the 
delthyrium  filled  by  the  beak  of  the  opposite  valve. 

Brachial  valve  subequally  or  a  little  less  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  surface  curving  abruptly 
to  the  cardinal  margin  and  more  gently  to  the  lateral  and  anterior  mar- 
gins, the  umbonal  region  rather  prominent  and  projecting  posteriorly  a 
little  beyond  the  hinge-line;  mesial  fold  absent  but  the  median  portion 
of  the  valve  is  slightly  flattened  towards  the  front ;  the  beak  strongly 
incurved  beneath  that  of  the  opposite  valve  and  nearly  or  quite  filling 
the  delthyrium  of  the  pedicle  valve. 

Surface  of  both  valves  marked  by  thin,  closely  crowded,  regular, 
imbricating  lamelhe  which  are  divided  into  flattened  spines,  of  which 
three  or  four  occupy  one  millimeter,  the  spines  of  successive  concentric 
rows  are  usually  uniform  in  position  and  are  consequently  rather  regularly 
arranged  in  radial  series;  when  partially  exfoliated  the  shell  is  marked 
only  by  the  fine  concentric  markings. 

Remarks. — This  species  is  so  closely  allied  to  C.  hirsuta  of  the  higher  beds 
of  the  Mississippian  series  that  there  is  perhaps  no  justification  in  con- 
sidering them  as  distinct.  A  careful  examination  of  all  examples  avail- 
able, however,  seems  to  indicate  that  the  concentric  rows  of  flattened 
spines  in  this  species  are  somewhat  finer,  more  regular  and  more  closely 


CLIOTIIYRIDINA  479 

crowded  than  in  typical  examples  of  C.  hirsuta.  The  shell  is  also  less 
apt  to  exhibit  the  slightly  pentagonal  ontline  which  is  commonly  assumed 
by  C.  hirsuta. 

Horizon. — Kinderhook  oolite  and  lower  Burlington  white  chert. 

Cliotiiyridina  hirsuta   (Hall) 
Plate  LXXX,  Figs.  13-24. 

1857.     Spirigera  hirsuta  Hall,  Trans.  Albany  Inst.,  vol.  4,  p.  8. 

1882.  Athyris  hirsuta  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1,  p.  49, 

pi.  6,  figs.  18-21. 

1883.  Athyris  hirsuta  Hall,  12th  Ann.  Kep.  Geol.  Surv.  Intl.,  p.  328,  pi. 

29,  figs.  18-21. 

1884.  Athyris  hirsuta  Walcott,  Pal.  Eureka  Dirt.,  p.  222,  pi.  18,  fig.  5. 

1894.  Cliothyris  Roysii  Hall  and  Clarke,  Int.  to  Study   of   Brack.,  pt.  2, 

pi.  35,  fig.  9  (not  fig.  10). 

1895.  Cliothyris  Roysii  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  46, 

fig.  23   (not  fig.  24). 
1895.     Cliothyris  hirsuta  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  46, 

figs.  25-28. 
1906.     Cleiothyris  hirsuta  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Inch.  p.  1320, 

pi.  19,  figs.  1-la;  pi.  22,  figs.  18-21. 

Description. — Shell  small,  lenticular,  suborbicular,  subquadrangular  or 
subpentagonal  in  outline,  length  and  breadth  usually  subequal,  the  great- 
est width  at  about  the  mid-length  of  the  shell;  hinge-line  much  shorter 
than  the  greatest  width  of  the  shell,  cardinal  extremities  rounded,  the 
two  valves  subequally  convex.  The  dimensions  of  a  specimen  of  average 
size  are:  length  9  mm.,  width  9.2  mm.,  thickness  6  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curv- 
ing abruptly  from  the  umbonal  region  to  the  cardinal  margin  and  more 
gently  to  the  lateral  and  anterior  margins ;  the  beak  small,  slightly  in- 
curved, pierced  by  a  subcircular  foramen  which  lies  in  a  plane  oblique  to 
the  plane  of  the  valves;  delthyrium  broad,  filled  by  the  beak  of  the 
opposite  valve,  connected  with  the  foramen  at  its  apex;  mesial  sinus 
obsolete,  but  in  some  of  the  larger  examples  the  mesial  portion  of  the 
shell  is  slightly  flattened. 

Brachial  valve  nearly  equally  convex  with  the  pedicle,  the  greatest 
convexity  posterior  to  the  middle,  the  surface  curving  abruptly  from 
the  point  of  greatest  convexity  to  the  cardinal  margin,  and  more  gently 
to  the  lateral  and  anterior  margins ;  mesial  fold  obsolete  or  represented 
only  by  a  narrow,  median,  flattened  region  which  is  more  or  less  ill- 
defined  laterally ;  beak  strongly  incurved  beneath  that  of  the  opposite 
valve,  and  nearly  or  quite  filling  the  delthyrium  of  that  valve. 

The  surface  markings  of  both  valves  consist  of  thin,  crowded,  con- 
centric,   closely    imbricating,    lamellose    extensions    of    the    shell,    which 


480  Mississippi  AN    BRACHIOPODA 

are  divided  into  flattened  spines,  about  three  of  winch  occupy  1  mm., 
the  spines  of  successive  rows  are  usually  somewhat  regularly  arranged 
in  radial  series  so  that  the  surface  of  the  shell,  when  liol  exfoliated,  lias 
the  appearance  of  being  finely  costate. 

Remarks. — This  species  exhibits  considerable  variation  in  size,  although  in 
its  more  typical  form  it  rarely  exceeds  10  num.  in  length.  The  propor- 
tional dimensions  of  (he  shell  are  also  somewhat  variable,  the  width 
being  sometimes  greater  and  sometimes  less  than  the  length,  though 
the  width  is  more  commonly  equal  to  or  a  little  greater  than  the  length. 
The  species  is  most  common  and  has  its  most  typical  development  in  the 
fauna  of  the  Salem  limestone,  but  it  occurs  also  in  beds  both  higher 
and  lower  than  that  horizon.  The  species  most  closely  resembles  C. 
parvirostra,  hut  if  is  smaller  and  usually  more  nearly  subcircular  in  outline, 
although  C.  parvirostra  has  sometimes  been  interpreted  as  a  large  form  of 
('.  hirsuta.  The  species  also  resembles  C.  sublamellosa,  but  besides  being  a 
smaller  species  its  valves  are  subequally  convex,  while  the  brachial  valve  of 
C.  sublamellosa  is  notably  more  convex  than  the  pedicle.  It  is  not  improba- 
ble that  the  young  individuals  of  C.  sublamellosa  have  more  nearly  equally 
convex  valves  than  the  mature  shells,  and  that  those  individuals  in  the 
Chester  which  have  sometimes  been  identified  as  C.  hirsuta  are  in  reality 
the  young  of  S.  sublamellosa. 

Horizon. — Warsaw  formation,  Salem  limestone,  Ste.  Genevieve  limestone. 

(  'l.IUTIIYRIDINA    I.KNTKTLAKIS    11.    Sp. 

Plate  LXXX,  Figs.  25-30 

Description. — Shell  small,  lenticular  in  form,  subelliptical  to  subpen- 
tagonal  in  outline,  the  width  greater  than  the  length,  the  hinge-line 
much  shorter  than  the  greatest  width  of  the  shell.  The  dimensions  of 
two  individuals  are:  length  10  mm.  and  11  mm.,  width  10.5  mm.  and 
13.3  mm.,  thickness  5.8  mm.  and  6  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle,  the  surface  slightly  compressed  towards  the  cardinal  ex- 
tremities, curving  rather  abruptly  from  the  point  of  greatest  convexity  to 
the  cardinal  margin  and  more  gently  to  the  lateral  margins,  in  the 
median  portion  the  surface  of  the  valve  curves  with  increasing  convexity 
to  the  anterior  margin ;  mesial  sinus  obsolete  except  towards  the  front 
of  the  valve,  where  a  broad,  flattened  area  is  developed  which  is  depressed 
slightly  or  not  at  all  below  the  general  surface,  anteriorly  this  flattened 
area  curves  somewhat  abruptly  towards  the  opposite  valve  and  is  pro- 
duced beyond  the  general  outline  of  the  valve ;  the  beak  small,  a  little 
incurved,  pierced  by  a  subcircular  foramen ;  cardinal  area  obsolete,  the 
delthyrium  connecting  with  the  foramen  at  its  apex,  filled  by  the  beak 
of  the  opposite  valve. 


CLIOTHYRIDIXA  481 

Brachial  valve  equally  or  a  little  more  convex  than  the  pedicle,  greatest 
convexity  posterior  to  the  middle,  the  surface  curving  abruptly  from 
the  point  of  greatest  convexity  to  the  cardinal  margin,  and  more  gently 
to  the  anterior  margin,  laterally  from  the  median  line  the  surface  is  at 
first  convex  and  then  becomes  straight  or  rather  strongly  concave,  the 
lateral  slopes  of  the  valve  being  compressed,  in  extreme  n,ases  strongly 
so ;  the  mesial  fold  broadly  rounded,  ill-defined  laterally,  most  elevated 
in  front,  in  those  specimens  with  the  lateral  slopes  of  the  valve  strongly 
compressed  the  broad,  ill-defined  fold  extends  well  towards  the  beak  ;  beak 
strongly  incurved,  filling  the  delthyrium  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  crowded,  concentric  rows  of  closely 
imbricating,  fine  spines,  which  are  usually  more  or  less  completely  eroded 
except  towards  the  anterior  and  lateral  margins  of  the  shell.  These 
spines  are  in  such  close  contact  with  the  surface  of  the  shell,  at  times, 
as  to  give  it  the  appearance  of  bein^;  finely  costate  towards  the  margin. 

Remarks. — This  species  is  most  closely  allied  to  C.  hirsuta,  and  perhaps 
might  not  be  considered  as  distinct  from  it  by  some  observers.  It  differs 
from  that  species  in  being  proportionally  much  thinner,  in  having  the 
broad,  anterior,  mesial  flattening  of  the  pedicle  valve  produced  towards 
the  opposite  valve  in  front,  in  the  compressed  lateral  slopes  of  the 
brachial  valve,  and  in  the  finer  surface  spines.  The  species  has  been  ob- 
served only  in  the  St.  Louis  limestone,  where  it  sometimes  occurs  in 
great  numbers  upon  the  surface  of  the  limestone  in  partings  between 
beds.  The  specimens  are  apt  to  be  much  crushed  and  flattened,  and  the 
true  form  of  the  shell  is  only  occasionally  found. 

Horizon. — St.  Louis  limestone. 


( 'ijothyridina  parvirostris  (Meek  and  Worthen) 
Plate  LXXVIII,  Fig.  25;  Plate  LXXX,  Figs.  61-66 

1860.     Athyris  parvirostra  Meek  and  Worthen,  Proe.  Acad.  Xat.  Sci.  Phil., 

p.  451. 
1866.     Athyris  planosulcata  ?  Meek  and  AVorthen,  Geol.  Surv.  111.,  vol.  2, 

p.  254.  pi.  18,  figs.  8a-d. 

Description. —Shell  below  medium  size,  lenticular,  subcircular  to  sub- 
pentagonal  in  outline,  the  length  and  breadth  subequal,  the  greatest  width 
Dear  the  mid-length  of  the  shell.  The  dimensions  of  a  nearly  complete 
specimen  are:  length  of  pedicle  valve  lit  mm.,  length  of  brachial  valve 
IS  mm.,  width  18.5  mm.,  thickness  11.5  mm. 

Pedicle  valve  most  convex  near  or  posterior  to  the  middle,  the  surface 
curving  abruptly  to  the  cardinal  margin  and  more  gently  to  the  lateral 
and  anterior  margins;  beak  .small,  incurved,  perforated  by  a  small  sub- 
circular   foramen   which   encroaches   upon   the   umbonal   portion   of   the 

—16 


t82  M  ISSISSI I'I'IAN    BBACHIOPODA 

valve;  delthyrium  filled  with  the  beak  of  the  opposite  valve,  joined  with 
Hie  foramen  al  its  apex;  mesial  sinus  wanting,  the  mesial  portion  of 
the  valve  sometimes  slightly  flattened,  and  the  anterior  margin  a  little 
prod  need. 

Brachial  valve  about  equally  convex  with  the  pedicle,  the  greatest  con- 
vexity neai'  or  a  little  posterior  to  the  middle,  the  surface  curving  rather 
abruptly  to  the  cardinal  margin  and  more  gently  to  the  lateral  and 
anterior  margins;  mesial  fold  wanting,  the  mesial  portion  of  the  valve 
sometimes  slightly  flattened;  the  beak  strongly  incurved  beneath  that 
of  the  opposite  valve  and  nearly  filling  the  delthyrium. 

The  surface  of  both  valves  marked  by  thin,  concentric,  closely  imbri- 
cating, lamellar  extensions  which  are  divided  into  flattened  spines,  al- 
though, as  commonly  preserved,  Ihese  surface  characters  have  been 
removed  by  exfoliation. 

Remarks. — This  species  is  most  closely  related  to  C.  hirsuta  and  C. 
:,iibliiiin  llosa.  From  the  first  of  these  it  differs  in  its  larger  size,  usually 
in  its  more  subpentagonal  outline,  and  often  in  the  slight  extension  of  the 
anterior  margin  of  the  pedicle  valve,  although  without  the  development  of 
a  mesial  sinus.  In  size  the  species  is  similar  to  C.  sublamellosa,  but  it  differs 
from  that  species  in  having  the  valves  subequally  convex  instead  of 
having  the  brachial  valve  notably  more  convex  than  the  pedicle.  The 
species  has  sometimes  been  referred  to  the  European  Athyris  planosulcata, 
hut  that  species  differs  from  C.  parvirostris  and  other  members  of  the 
genus  Cliothyridina,  in  having  the  concentric  lamelke  of  the  shell  entire, 
not  divided  into  spines,  a  condition  which,  so  far  as  external  characters 
are  concerned,  would  throw  that  species  into  the  genus  Atrypa  in  its  strict 
sense.  The  concentric  lamella?  of  A.  planosulcata,  however,  are  distinctly 
ribbed,  and  these  ribs  are  only  one  step  removed  from  the  concentric  rows 
of  spines  in  Cliothyridina.  Exfoliated  specimens  of  A.  planosidcata  and 
C.  parvirostris  would  perhaps  be  indistinguishable,  since  the  general  pro- 
portions of  the  two  shells  are  much  alike. 

Horizon. — Keokuk  limestone. 

Cliothyridina  sublamellosa  (Hall) 
Plate  LXXX,  Figs.  31-60 

1858.     Athyris  sublamellosa  Hall,  Geol.  Iowa,  vol.  1,  pt,  2,  p.  702,  pi.  27, 

figs.  la-c. 
1861.     Athyris  obvia  McChesney,  Desc.  New  Spec.  Foss..  p.  81. 
1863.     Spirigera  Clintonensis  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2, 

p.  89. 
1863.     Spirigera  Americana  Swallow,  Trans.  St.  Louis  Acad.  Sci.,  vol.  2, 

p.  89. 
1894.     Athyris  sublamellosa  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  92. 


CLIOTHYRIDINA  483 

3894.     Cliotltyris  Koyssi  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2, 

pi.  35,  fig.  10  (not  fig.  9). 
1895.     Cliothyris  Royssi  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  4ti, 

fig  24  (not  fig.  23). 
19  LI.     Cleiothyris  hirsuta  Morse,  Proe.  Ohio  State  Aead.  Sei.,  vol.  5,  p.  388, 

fig.  15. 

Description. — Shell  below  medium  size,  usually  longer  than  wide,  the 
greatest  width  near  or  posterior  to  the  mid-length,  sometimes  wider  than 
long,  suborbieular  or  subovate  in  outline,  the  hinge-line  much  shorter 
than  the  greatest  width,  both  valves  convex,  the  brachial  valve  usually 
more  convex  than  the  pedicle  and  sometimes  notably  so.  The  dimensions 
of  an  average  specimen  are :  length  19.5  mm.,  width  20.5  mm.,  thickness 
12  mm. 

Pedicle  valve  moderately  convex,  the  greatest  convexity  posterior  to 
the  middle  of  the  valve  in  the  umbonal  region,  the  surface  curving  ab- 
ruptly from  the  umbonal  region  to  the  cardinal  margin  and  gently 
towards  the  lateral  and  anterior  margins,  often  compressed  or  even  con- 
cave towards  the  lateral  margins ;  beak  not  prominent,  but  slightly  ex- 
tended beyond  that  of  the  opposite  valve,  only  slightly  incurved,  perfor- 
ated by  a  subcircular,  oblique  foramen  which  opens  into  the  delthyrium 
posteriori}' ;  mesial  sinus  obsolete  in  smaller  individuals  and  sometimes 
obscure  in  full  grown  examples,  but  often  well  developed  towards  the  an- 
terior margin  of  the  valve  where  it  is  rather  narrow  and  of  moderate 
depth,  rounded  in  the  bottom  and  ill-defined  laterally. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
posterior  to  the  middle,  the  surface  curving  rather  abruptly  from  the 
point  of  greatest  convexity  towards  the  cardinal  margin,  and  more  gently 
to  the  lateral  and  anterior  margins,  the  convexity  extending  out  to  the 
lateral  margins  or  sometimes  slightly  compressed  laterally ;  the  beak  in- 
curved beneath  that  of  the  opposite  valve,  and  more  or  less  completely 
filling  the  delthyrium ;  mesial  fold  obscure  except  sometimes  near  the  an- 
terior margin,  when  best  developed  it  consists  of  a  narrow,  mesial  flat- 
tened area  more  or  less  illdefined  laterally,  and  not  distinctly  elevated 
above  the  general  surface  of  the  valve  except  sometimes  near  the  anterior 
margin. 

The  surface  markings  of  both  valves  consist  of  broad,  thin,  concentric 
lamellose  expansions  of  the  shell  which  are  divided  nearly  to  the  base 
into  flattened  spines,  about  three  of  which  occupy  the  space  of  one  milli- 
meter. 

h'(  murks. — This  species  is  one  of  the  conspicuous  members  of  the  lower 
Chester  faunas,  and  may  be  readily  recognized  on  account  of  the  greater 
convexity  of  the  brachial  valve.  In  shale  beds  the  surface  ornamentation 
is  not  infrequently  more  or  less  perfectly  preserved,  but  in  the  limestones 
these  characters  are  all  destroyed  by  exfoliation  in  removing  the  speci- 


4S4  MISSISSIPPIAN    BBACHIOPODA 

mens  from  the  matrix.  The  stronger  developmenl  of  the  fold  and  sinus 
towards  the  anterior  margin  of  the  shell,  and  the  concavity  of  the  pedicle 
valve  towards  the  lateral  margins,  are  characters  produced  almost  entirely 
bj  i  lit*  developmenl  of  the  concentric  lameuose  expansions  from  the 
shell,  when  these  are  removed  both  of  these  characters  largely  disappear. 
In  the  original  description  of  the  species  the  absence  of  a  distind  mesial 
sinus  in  the  pedicle  valve  is  mentioned,  and  lliis  is  true  in  specimens, 
Such  as  are  illustrated  by  Hall,  which  have  for  the  most  pari  lost  their 
eoneent  ric  lamella'. 

Tlie  shell  described  by  McChesney  as  Athyris  dbvia  is  said  to  differ  from 
('.  sublamellosa  in  having  the  pedicle  valve  deeper  than  the  brachial.  The 
type  of  McChesney's  species  is  lost,  and  in  his  later  publications  the 
species  is  not  figured  and  is  not  even  mentioned,  suggesting  that  it  was 
abandoned  by  the  author.  The  species  was  described  from  the  Chester 
limestone,  but  late  collections  have  shown  that  no  such  form  is  commonly 
present  in  the  fauna  of  that  formation  which  can  lie  considered  as  distinct 
I  idiii  C.  sublamellosa,  although  individuals  sometimes  occur  having  the 
pedicle  valve  most  convex,  a  condition  usually  due  to  the  distortion  of 
the  shell.  It  therefore  seems  safe  to  consider  McChesney's  species  either 
as  unrecognizable  or  as  a  synonym  of  ('.  sublamellosa. 

The  two  species  described  from  the  Chester  formation  by  Swallow  as 
Spirigera  clintonensis  and  S.  americana  are  clearly  synonyms  of  C.  sub- 
lamellosa,  although  the  types  of  the  species  are  apparently  lost  and  cannot 
be  studied.  The  description  of  S.  americana  exactly  fits  the  usual  form  of 
C.  sublamellosa,  and  it  is  not  infrequently  possible  to  select  examples  having 
a  somewhat  greater  width  than  usual  which  correspond  closely  with  the 
description  of  S.  clintonesis. 

Horizon. — Ste.  Genevieve  limestone  and  Chester  group. 

Genus  COMPOSITA   Brown 

Description. — Shells  small  or  of  medium  size,  subovate,  subquadrangu- 
lar  to  subpentagonal  in  outline,  the  valves  biconvex,  with  the  fold  and 
sinus  developed  in  the  anterior  portion  of  the  shell  or  sometimes  extend- 
ing posteriorly  to  the  umhonal  region,  both  the  fold  and  the  sinus  may 
be  marked  by  a  rather  sharp  mesial  sulcus.  The  surface  of  the  valves 
smooth  or  marked  only  by  concentric  lines  of  growth  which  are  never 
extended  into  lamellae.  The  beak  of  the  pedicle  valve  incurved  so  as  to 
conceal  the  delthyrium,  but  the  foramen  is  usually  exposed,  encroaching 
upon  the  umhonal  region  of  the  valve.  Internally  the  dental  lamella1 
and  muscular  scars  resemble  those  of  Athyris,  but  with  the  diductor 
impressions  usually  more  faintly  developed.  In  the  brachial  valve  the 
hinge-plate  is  similar  to  that  of  Athyris,  but  with  its  posterior  margin 


COMPOSITA  485 

extended  posteriorly  beyond  the  margin  of  the  valve  into  the  umbonal 
cavity  of  the  opposite  valve;  the  brachidium,  including  the  jugum,  with 
its  accessory  lamellae  similar  to  that  of  Athyris. 

Remarks. — This  genus  is  usually  more  ovate  or  subquadrangular  than 
cither  Athyris  or  Cliothyridina,  but  its  most  essential  differential  char- 
acter is  found  in  the  character  of  the  surface  markings,  the  lines  of 
growth  being  extended  into  neither  continuous  nor  fimbriate  lamellae. 
These  shells  have  been  commonly  designated  under  the  generic  name 
Seminula  since  the  publication  of  Hall  and  Clarke's1  great  work  on  the 
genera  of  Paleozoic  Brachiopoda,  but  Buckman  has  shown2  that  the  geno- 
type of  McCoy's  Seminula  is  a  shell  allied  to  Camarophoria,  and  that  the 
name  is  consequently  inapplicable  to  this  group  of  shells,  and  he  has 
adopted  the  name  Composita  Brown,  which  was  based  upon  shells  of  this 
type. 

The  members  of  the  genus  compose  an  assemblage  of  forms  between 
which  it  is  exceedingly  difficult  to  draw  sharp,  specific  lines.  Those  mem- 
bers of  the  genus  from  the  middle  and  upper  Mississippian  faunas  of 
the  Mississippi  valley  basin  are  usually  referred  to  one  of  two  species, 
('.  in  nucha  or  C.  subquadrata.  The  first  of  these  was  originally  described 
from  the  Salem  limestone  fauna  of  Indiana  and  Illinois,  the  second  from 
the  Chester  fauna  of  Illinois.  An  examination  of  a  large  number  of 
individuals  from  these  two  horizons,  from  both  the  original  and  other 
localities,  shows  that  series  can  be  selected  which  pass  with  complete 
gradation  from  one  form  to  the  other.  Aside  from  these  two  commonly 
recognized  forms,  an  extended  series  of  specimens  shows  several  others 
which  if  isolated  would  be  recognized  by  any  one  as  distinct  specific 
forms,  but  like  the  two  already  mentioned,  they  merge  with  complete 
gradation  into  the  general  type.  In  addition  to  these  forms  the  Penn- 
sylvanian  C.  subtil  Ha  is  united  by  regular  gradations  with  these  Missis- 
sippian shells.  Under  these  circumstances  the  student  is  forced  to  one  of 
two  conclusions,  he  must  either  unite  all  of  these  forms  into  one  exceed- 
ingly variable  species,  or  he  must  recognize  several  specific  or  varietal 
groups  which  grade  into  each  other.  The  last  of  these  methods  appeals 
most  strongly  to  the  writer,  and  preference  is  given  to  the  recognition  of 
the  groups  as  of  specific  rank,  there  being  little  utility  in  giving  a  par- 
ticular shell  three  names,  when  two  will  serve  as  well.  Among 
a  group  of  any  considerable  number  of  individuals  of  these  shells,  from 
a  single  horizon  and  locality,  there  is  always  a  central  form,  a  sort  of  com- 
posite of  all  those  individuals,  represented  by  the  average  of  the  sum 
total  of  characters,  which  is  the  true  ideal  of  the  species.  It  matters 
not  that  a  few  of  the  individuals  agree  essentially  in  all  their  characters 

l  Pal.  N.  Y.,  vol.  8,  pt.  2,  p.  93.     (1894.) 

-'  Ann.  and  Mag.  Nat.  Hist.,  ser.  7,  vol.  18,  p.  325.    (1906.) 


4Sti  MISSISSIPPIAN    BRACHIOPODA 

with  ;i  lew  individuals  from  ji ii<>t li<»i-  specific  group  from  another  locality 
and  horizon.  The  important  fact  is  the  central,  average  type  of  shell,  and 
as  many  such  types  as  can  be  clearly  recognized  are  worthy  of  specific 
recognition.  The  gradation  of  these  types  into  each  other  at  their  ex- 
tremes is  indication  only  of  the  close  and  probable  genetic  relationship 
of  the  forms  and  probably  of  the  youth  of  the  generic  type.  With  this 
interpretation  of  the  genus  it  will  not  infrequently  be  found  to  be  difficult 
or  even  impossible  to  identify  specifically  certain  individual  specimens, 
and  specific  identifications  will  necessarily  be  made  from  groups  of  in- 
dividuals. 

CoMPOSITA    TRINUCLEA    (Hall) 

Plate  LXXXI,  Figs.  16-45 

1856.     T<  nbrat  ii  I  it  I  riii  ml  in  Hall,  Trans.  Alb.  Inst.,  vol.  4,  p.  7. 
1858.     T<  nbraliila  trinuclea  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  659,  pi.  23 
figs.  4a-c,  5. 

1882.  Athyris  trinuclnis  Whitfield,  Bull.  Am.  Mus.  Nat.  Hist.,  vol.  1,  p 

50,  pi.  6,  figs.  22-27. 

1883.  Atliyris  trinucleus   Hall.  12th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  329 

pi.  29,  figs.  22-27. 
1891.    Athyris  subquadrata  Whitfield,  Am.  N.  Y.  Acad.  Sci.,  vol.  5,  p.  585 

pi.  14,  figs.  1-3. 
1894.     Scmimda  trinuclea  Hall  and  Clarke,  Int.  to  Study  of  Brach.,  pt.  2 

pi.  35,  figs.  11,  12,  14. 
1S94.     Seminula  subquadrata  Hall  and  Clarke,  Int.  to  Study  of  Brach. 

pt.  2,  pi.  35,  figs.  13,  15. 

1894.  Athyris  trinuclea  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  92. 

1895.  Athyris  subquadrata  Whitfield,  Geol.  Surv.  Ohio,  vol.  7,  p.  472,  pi 

10,  figs.  1-3. 
1895.     Seminula  trinuclea  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2,  pi.  47 

figs.  5,  6,  10-14. 
1895.     Seminula  subquadrata  Hall  and  Clarke,  Pal.  N.  Y.,  vol.  8,  pt.  2 

pi.  47,  figs.  7-9,  15,  16;  pi.  84,  figs.  30-31. 
1897.     Athyris  subquadrata  Weller,  Trans.  N.  Y.  Acad.  Sci.,  vol.  16,  p.  258 

pi.  18,  fig.  16. 
1903.     Seminula  subquadrata  f  Girty,  U.  S.  Geol.  Survey,  Prof.  Paper,  No 

16,  p.  296,  pi.  1,  fig.  5. 
1906.     Seminula  trinuclea  Beede,  30th  Ann.  Rep.  Geol.  Surv.  Ind.,  p.  1322 

pi.  22.  figs.  22-27. 
1909.     Seminula  subquadrata  Bassler,  Va.  Geol.  Surv.,  Bull.  No.  II  A,  pi 

29,  figs.  6-8. 
1909.     Seminula  trinuclea  Bassler,  Va.  Geol.  Surv.,  Bull.  No.  II  A,  pi.  29 

figs.  9-10. 
1911.     Seminula  subquadrata  Morse,  Proe.  Ohio  State  Acad.  Sci.,  vol.  5 

p.  383,  figs.  13a-c. 

Description. — Shell  usually  small,  always  below  medium  size,  subovate 
in  outline,  the  larger  specimens  sometimes  becoming  subquadrate  or  sub- 
pentagonal,  the  width  usually  less  than  the  length,  but  sometimes  equal 


COMPOSITA  487 

to  oi'  greater  than  the  length,  the  greatest  width  near  or  anterior  to  the 
mid-length  of  the  shell,  the  fold  and  sinus  usually  well  developed  anter- 
iorly. The  dimensions  of  three  examples  from  the  Salem  limestone  are : 
length  8.9  mm.,  13.8  mm.  and  18.5  mm.,  width  8  mm.,  12.7  mm.,  and  19.5 
mm.,  thickness  6  mm.,  9  mm.  and  10.8  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  from  the  umbonal  region  to  the  cardinal  margin,  and  also  in 
the  narrower  examples  to  the  lateral  margins,  the  curvature  from  the 
beak  to  the  front  margin  becoming  regularly  less  convex  anteriorly;  the 
mesial  sinus  originating  at  or  near  the  beak  as  a  narrow,  flattened  or 
slightly  depressed  line,  anteriorly  it  becomes  stronger,  in  the  narrower 
examples  it  is  rounded  in  the  bottom,  in  the  wider  forms  it  is  broader 
and  often  with  a  more  or  less  distinct  groove-like  furrow  along  the 
median  line,  the  lateral  margins  of  the  sinus  are  ill-defined,  but  in  some 
examples,  especially  the  broader  ones,  there  is  a  more  or  less  well-defined 
furrow  upon  each  lateral  slope  of  the  valve,  a  little  outside  of  the  margin 
of  the  sinus  and  parallel  to  it,  these  furrows  sometimes  originating  in  the 
umbonal  region  and  becoming  stronger  towards  the  anterior  margin ; 
the  beak  more  or  less  strongly  incurved,  truncated  obliquely  to  the  plane 
of  the  valve,  and  perforated  by  a  large  subcircular  foramen ;  cardinal 
area  obsolete,  the  delthyrium  broadly  triangular,  connected  at  its  apex 
with  the  foramen,  nearly  or  quite  filled  by  the  beak  of  the  opposite  valve. 

Brachial  valve  somewhat  trilobate,  about  equally  convex  with  the 
pedicle,  the  greatest  convexity  usually  near  the  middle ;  mesial  fold 
usually  originating  in  the  umbonal  region,  only  weakly  developed  in  the 
posterior  half  of  the  shell,  becoming  more  prominent  in  front,  in  the 
narrower  forms  it  is  rounded  on  top,  but  in  the  broader  individuals  it  is 
flatter  and  is  sometimes  marked  by  a  narrow,  shallow,  median  furrow 
which  originates  near  the  middle  of  the  shell  and  continues  to  the  front 
margin,  on  each  side  of  the  fold  in  the  more  strongly  trilobed  forms 
there  is  a  rounded  sinus,  originating  near  the  middle  of  the  valve  and 
increasing  in  strength  towards  the  front,  the  lateral  slopes  curving  more 
or  less  abruptly  to  the  lateral  margins ;  beak  strongly  incurved  beneath 
that  of  the  opposite  valve  and  nearly  or  quite  filling  the  delthyrium. 

The  surface  of  both  valves  is  marked  by  more  or  less  regular  con- 
centric lines  of  growth  which  are  sometimes  crowded  toward  the  front, 
otherwise  the  surface  of  the  shell  is  smooth. 

h't  marks. — This  species  is  an  exceedingly  variable  one,  and  extreme 
forms,  if  found  separate  and  isolated,  would  be  considered  without  hesi- 
tation as  distinct  species.  The  variation  in  size  is  considerable,  the 
smaller  specimens  from  the  diminutive  Spergen  Hill  fauna  sometimes 
being  less  than  5  mm.  in  length,  although  apparently  adult  individuals. 
The  larger  examples  are  often  as  much  as  20  mm.  in  length.     The  propor- 


188  .MISSISSIPPI AN    BBACHIOPODA 

tional  width  and  thickness  of  the  shells  is  also  extremely  variable.  The 
diminutive  individuals  from  the  Spergen  Hill  Fauna  are  apt  to  be  more 
globular  than  the  Larger  ones.  The  mesial  furrow,  present  sometimes  in 
both  fold  and  sinus,  is  a  variable  character,  as  are  also  the  furrows  outside 

tile   lateral    margins  of  the  sinus  of  the   pedicle   valve. 

A  nearly  related  species  is  ('.  subquadruta  from  the  Chester  fauna,  and 
specimens  here  referred  to  C.  trinwlea  have  frequently  been  called  C.  sub- 
quadrata,  in  fact  these  two  mimes  have  sometimes  been  considered  as 
synonyms.  There  seems  to  lie  a  constant  difference  between  the  two 
forms,  however,  in  the  more  posterior  extension  of  the  mesial  sinus  of  the 
pedicle  valve  in  ('.  trinuclt <t. 

Horizon, — Salem  limestone,  St.  Louis  limestone,  Ste.  Genevieve  lime- 
stone. ( Ihester  group. 

COMPOSITA  LEWISENSIS  Q.  sp. 

Plate  LXXX1,  Figs.  46-51 

Description. — Shell  small,  ovate-subpentagonal  in  outline,  longer  than 
wide,  the  greatest  width  anterior  to  the  mid-length.  The  dimensions  of 
two  nearly  complete  specimens  are:  length  of  pedicle  valve  10.4  mm.  and 
10.6  mm.,  length  of  brachial  valve  !).6  mm.  and  9.6  mm.,  greatest  width 
9.4  mm.  and  9.2  mm.,  thickness  6.8  mm.  and  6.2  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  postero-lateral  margins,  becoming  inflected  to  the  car- 
dinal extremities  and  curving  much  more  gently  to  the  antero-lateral  and 
anterior  margins;  mesial  sinus  inconspicuous,  usually  originating  near  or 
in  front  of  the  middle  of  the  valve,  very  shallow,  rounded  in  the  bottom, 
ill-defined  at  its  lateral  margins;  the  beak  small,  pointed,  rather  strongly 
incurved,  perforated  by  a  subcircular  foramen  which  encroaches  wholly 
upon  the  umbonal  region  of  the  valve ;  cardinal  area  obsolete,  the  delthy- 
rium  closed. 

Brachial  valve  subequally  or  a  little  less  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  surface  curving  rather 
abruptly  to  the  postero-lateral  margins  and  more  gently  to  the  antero- 
lateral and  anterior  margins ;  mesial  fold  obsolete,  the  mesial  portion  of 
the  valve  usually  obscurely  flattened  anteriorly  from  the  middle,  and 
sometimes  very  slightly  depressed  towards  the  front  margin  to  form  a 
slight  sinus  which  is  fainter  and  more  obscure  than  that  of  the  opposite 
valve ;  beak  pointed,  strongly  incurved  beneath  that  of  the  opposite  valve 
and  partially  filling  the  delthyrium. 

Surface  of  both  valves  marked  by  somewhat  regular,  concentric  lines 
of  growth  which  are  sometimes  nearly  obsolete  except  near  the  anterior 
margin. 

Remarks. — This  little  shell  is  characterized  by  the  absence  of  a  mesial 
elevation  of  the  brachial  valve,  and  by  the  slight  mesial  sinus  of  the  ped- 


COMPOSITA  489 

iele  valve.  It  resembles  ('.  Icevis,  but  besides  being  a  somewhat 
thicker  shell  it  does  not  possess  the  distinct  sinus  of  the  brachial  valve 
and  the  consequent  anterior  emargination  of  that  species,  and  the  concen- 
tric lines  of  growth  are  much  more  conspicuous.  In  its  surface  markings 
the  species  most  closely  resembles  C,  trinuclea,  but  it  may  be  easily  dis- 
tinguished from  that  species  by  the  obsolete  fold  and  slight  sinus. 
Locality.— Patrick's  Quarry,  Middle  Fabius  River,  Lewis  Co.,  Mo. 

COMPOSITA  SUBQUADRATA    (Hall) 

Plate  LXXXI,  Figs.  1-15 

1858.     Athyris  subquadrata  Hall,  Geol.  Iowa,  vol.  1,  pt.  2,  p.  703,  pi.  27, 

figs.  2a-d ;  p.  708,  fig.  118. 
1.894.     Athyris  subquadrata  Keyes,  Mo.  Geol.  Surv.,  vol.  5,  p.  92. 

Description. — Shell  of  medium  size,  the  width  equal  to.  greater  than  or 
less  than  the  length,  subovate  or  subquadrate  in  outline,  the  greatest 
width  usually  a  little  anterior  to  the  mid-length  of  the  shell,  the  fold  and 
sinus  well  developed  anteriorly.  The  dimensions  of  four  specimens  are : 
length  27  mm.,  25  mm.,  25  mm.,  and  18.5  mm.;  width  27.5  mm.,  26.5  mm., 
24.5  mm.,  and  19  mm.;  thickness  17  mm.,  17  mm.,  17.5  mm.,  and  11.5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  median  line 
arched  from  the  beak  to  the  front  margin  with  a  decreasing  convexity 
anteriorly,  the  surface  curving  abruptly  from  the  umbonal  region  to  the 
cardinal  margin  and  much  more  gently  to  the  antero-lateral  margins :  the 
mesial  sinus  usually  obsolete  in  the  anterior  half  of  the  shell,  originating 
near  the  middle  of  the  valve  as  a  broad,  shallow,  ill-defined  depression, 
remaining  broad  and  shallow  to  the  front  of  the  shell  where  it  is  more  or 
less  produced  in  a  lingual  extension,  the  lateral  slopes  on  each  side  of  the 
sinus  convex;  the  beak  incurved,  truncated  obliquely  to  the  plane  of  the 
valve  and  perforated  by  a  large,  subcircular  or  subovate  foramen;  car- 
dinal area  obsolete,  the  delthyrium  broadly  triangular,  nearly  filled  by  the 
beak  of  the  opposite  valve. 

Brachial  valve  more  convex  than  the  pedicle,  the  greatest  convexity 
usually  in  front  of  the  middle,  the  surface  curving  rather  abruptly  to- 
wards the  cardinal  margin  and  much  more  gently  towards  the  front ; 
mesial  fold  nearly  or  quite  obsolete  posteriorly,  broadly  rounded  and 
more  or  less  elevated  in  front,  lateral  slopes  of  the  valve  convex  except 
where  they  curve  up  into  the  sides  of  the  median  fold ;  the  beak  strongly 
incurved,  filling  the  delthyrium  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  concentric  lines  of  growtli  which 
become  more  numerous  and  sometimes  crowded  towards  the  front  of  the 
shell. 

Remarks. — This  species  has  not  infrequently  been  confused  with  C.  trin- 
uclea,  as  here  interpreted,  but  it  differs  from  that  form  in  the  larger  size 


4!)0  MISSISSIIM'IAN    BBACHIOPODA 

of  the  niiil lire  shell,  in  the  greater  obsolescence  of  the  mesial  sinus  of  the 
pedicle  valve  towards  the  beak,  in  the  broader  and  flatter  sinus  ante- 
riorly. 

The  species  was  originally  described  from  Chester,  Illinois,  but  the  orig- 
inal type  of  the  species,  judging  from  the  illustrations  alone,  was  not  an 
entirely  typical  representative  as  shown  by  the  many  specimens  from 
Chester  which  have  come  under  the  observation  of  the  writer.  Hall's 
figure  2b  represents  a  shell  having  the  sinus  originating  much  nearer  the 
bealc  than  usual,  in  this  respect  simulating  C.  trinuclea,  the  lateral  slopes 
of  the  valves,  however,  do  not  show  the  distinct  trilobation  of  the  shell 
which  is  so  common  in  that  species.  Examples  of  the  Chester  shell  can 
be  selected  which  agree  almost  exactly  with  some  specimens  of  C.  trinuclea, 
but  the  average  characters  of  a  large  number  of  individuals  of  the  two 
forms  are  quite  different.  The  species  is  perhaps  just  as  closely  allied 
to  C.  argentea  of  the  Pennsylvanian  faunas,  it  is  of  about  the  same  aver- 
age size  but  usually  has  a  somewhat  flatter  mesial  sinus. 

Horizon. — Chester  group. 

COMPOSITA  SULCATA  n.   sp. 

Plate  LXXXII,  Figs.  1-10 

Description. — Shell  below  medium  size,  subquadrate  in  outline,  wider 
than  long,  the  greatest  width  near  the  mid-length  of  the  shell.  The  di- 
mensions of  a  nearly  complete  specimen  are:  length  of  pedicle  valve  20 
mm.,  length  of  brachial  valve  17.5  mm.,  greatest  width  23.9  mm.,  thick- 
ness 12  mm. 

Pedicle  valve  most  convex  in  the  umbonal  region,  the  surface  curving 
abruptly  and  becoming  a  little  inflected  to  the  cardinal  margin,  gently 
convex  from  the  umbo  to  the  antero-lateral  margins ;  beak  rather  short, 
incurved;  the  mesial  sinus  originating  at  or  near  the  beak,  increasing 
rapidly  in  depth  towards  the  front  where  it  becomes  very  profound  and  is 
produced  in  a  rounded  anterior  extension  of  the  valve,  it  is  illdefined  lat- 
erally and  its  width  in  front  is  sometimes  equal  to  one-half  the  total 
width  of  the  valve,  in  the  bottom  it  is  rounded  or  subangular. 

Brachial  valve  about  as  deep  or  a  little  deeper  than  the  pedicle,  its 
greatest  depth  near  the  middle,  the  surface  curving  somewhat  abruptly 
from  the  umbo  to  the  cardinal  margin,  gently  convex  from  the  umbo  to 
the  middle  of  the  lateral  margins  and  more  strongly  curved  to  the  antero- 
lateral margins ;  along  the  median  line  the  surface  is  convexly  curved  pos- 
teriorly, becoming  nearly  straight  posterior  to  the  middle  and  so  continu- 
ing to  the  front;  mesial  fold  little  or  not  at  all  differentiated  posteriorly, 
becoming  much  elevated  in  front,  not  sharply  defined  laterally  but  sep- 
arated from  the  lateral  slopes  by  a  distinct  sinuosity  of  the  shell  on  each 
side. 


COMPOSITA  491 

Surface  of  the  shell  marked  only  by  concentric  lines  of  growth  which 
are  sometimes  stronger  and  more  crowded  towards  the  outer  margin  of 
the  valves. 

Remarks.— This  species  differs  from  C.  subquadrata,  its  nearest  ally,  in 
its  much  deeper  sinus  towards  the  front,  a  character  which  is  more 
strongly  developed  in  this  species  than  in  any  other  member  of  the  genus 
here  defined. 

Horizon. — Chester  group. 

Composita  l^vis  n.  sp. 
Plate  LXXXII,  Figs.  14-20 

Description. — Shell  small,  longer  than  wide,  with  the  greatest  width 
anterior  to  the  middle,  subovate  in  outline,  with  the  anterior  margin 
emarginate.  The  dimensions  of  two  nearly  perfect  examples  are:  length 
of  pedicle  valve  12  mm.  and  10.7  mm.,  length  of  brachial  valve  11  mm. 
and  10  mm.,  greatest  width  10.3  mm.  and  9.3  mm.,  thickness  7.5  mm.  and 
6.5  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  postero-lateral  margins  and  strongly  inflected  to  the  car- 
dinal extremities,  the  curvature  much  more  gentle  to  the  antero-lateral 
and  anterior  margins ;  mesial  sinus  short,  originating  near  or  a  little  in 
front  of  the  middle,  either  remaining  shallow  or  attaining  a  moderate 
width  and  depth  at  the  anterior  margin;  the  beak  attenuate  and  mod- 
erately incurved,  coming  nearly  in  contact  with  the  umbo  of  the  opposite 
valve,  truncated  obliquely  to  the  plane  of  the  valve,  the  foramen  rather 
large,  elliptical  in  outline,  encroaching  entirely  upon  the  umbonal  por- 
tion of  the  valve,  the  delthyrium  filled  with  the  beak  of  the  opposite 
valve. 

Brachial  valve  subequally  or  a  little  more  convex  than  the  pedicle,  the 
greatest  convexity  posterior  to  the  middle,  the  umbo  prominent  and 
projecting  notably  posteriorly  beyond  the  hinge-line,  the  surface  curving 
abruptly  to  the  postero-lateral  margins  and  becoming  somewhat  inflected 
at  the  cardinal  extremities,  curving  more  gently  to  the  antero-lateral 
and  anterior  margins ;  mesial  portion  of  the  valve  somewhat  flattened 
anteriorly  from  the  middle,  usually  becoming  slightly  depressed  in  a 
short  and  shallow  median  sinus  near  the  anterior  margin,  which,  meeting 
the  sinus  of  the  opposite  valve,  produces  the  emargination  of  the  shell 
in  front;  beak  sharply  pointed  and  strongly  incurved  beneath  that  of 
the  opposite  valve. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  a  few  obscure, 
concentric  lines  of  growth  which  are  commonly  present  only  towards 
the  anterior  margin. 


4!i2  MISS1SSIPPIAN    BBACHIOPODA 

I,' i  marks. — This  species  is  characterized  by  the  prominence  of  the  umbo 
of  the  brachial  valve,  the  smoothness  of  the  surface,  the  shortness  of 

the  mesial  sinus  of  the  pedicle  valve  and  the  absence  of  a  mesial  fold 
in  the  brachial  valve,  in  place  of  which  the  surface  of  the  valve  is  flat- 
tened towards  the  front  and  usually  somewhat  depressed  in  a  slight 
mesial  sinus  (dose  to  the  front    margin. 

Horizon. — ( Ihester  group. 

Composite  pentagonia  q.  sp. 

Plate  LXXXII,   Figs.  52-57 

Description. — Shell  below  medium  size,  broader  than  long,  subpentag- 
onal  in  outline,  the  postero-lateral  margins  longer  than  the  other  sides 
of  the  pentagon  and  meeting  at  the  beak  in  an  angle  of  about  105  degrees, 
laterally  the  margins  are  rounded,  becoming  a  little  concave  antero- 
laterally,  the  anterior  margin  rather  short  and  emarginate.  The  dimen- 
sions of  two  very  perfect  internal  casts  are:  length  of  pedicle  valve  15.5 
mm.  and  14. S  mm.,  length  of  brachial  valve  14  mm.  and  12.8  mm.,  greatest 
width  16.:]  mm.  and  16.5  mm.,  thickness  11  mm.  and  10.3  mm. 

Pedicle  valve  convex  in  the  umbonal  region,  the  surface  curving  ab- 
ruptly as  it  approaches  the  postero-lateral  margins,  and  in  the  internal 
casts  a  little  incurved  to  the  cardinal  extremities,  towards  the  antero- 
lateral margins  the  surface  is  regularly  convex  and  along  the  median 
line  from  beak  to  front  it  describes  nearly  a  semicircle;  mesial  sinus  orig- 
inating near  the  middle  of  the  valve,  shallow,  of  moderate  width,  and 
rounded  in  the  bottom,  laterally  its  surface  rounds  regularly  into  the 
lateral  slopes  of  the  valve  so  it  is  not  sharply  defined;  the  beak  strongly 
incurved,  the  foramen  apparently  rather  small,  the  delthyrium  filled 
with  the  beak  of  the  opposite  valve.  Internally  the  dental  lamella3  are 
rather  strong  and  reach  anteriorly  from  the  beak  from  one-fifth  to  one- 
fourth  the  length  of  the  valve. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  its  greatest  con- 
vexity near  or  a  little  posterior  to  the  middle,  the  surface  curving  more 
abruptly  to  the  postero-lateral  margins,  more  gently  to  the  antero-lateral 
and  anterior  margins ;  mesial  fold  originating  near  the  middle  of  the  valve, 
low,  flattened  on  top  and  towards  the  front  depressed  in  a  slight  longi- 
tudinal sinus  producing  the  emargination  of  the  anterior  margin  of  the 
shell,  laterally  the  fold  is  bounded  by  slight  depressions  more  notice- 
able towards  the  front,  which  produce  the  concavity  or  emargination  of 
the  antero-lateral  margins  of  the  shell;  the  beak  strongly  incurved  be- 
neath that  of  the  opposite  valve. 

Surface  of  both  valves,  as  seen  in  the  internal  casts,  marked  only  by 
rather  strong,  somewhat  irregular,  concentric  lines  of  growth  towards 
the  front. 


COMPOSITA  493 

Remarks. — This  species  has  been  established  upon  two  very  perfect 
internal  casts  from  chert,  which  differ  so  notably  from  other  allied 
athyroid  shells  in  form  and  general  proportions  that  one  is  forced  to 
consider  them  as  specifically  distinct.  They  resemble,  in  some  degree, 
some  of  the  shells  referred  to  Athyris  ambigua  by  British  paltontologists, 
but  the  interpretation  of  this  species  lias  commonly  been  so  broad  as  to 
include  almost  all  species  of  Composita.  In  these  internal  casts  the 
external  surface  characters  are,  of  course.  Lacking,  but  the  shells  must 
have  possessed  very  strong  concentric  lines  of  growth  towards  the  front 
because  they  are  so  well  exhibited  even  upon  the  internal  casts;  whether 
or  no  they  also  possessed  other  markings  is  not  possible  to  determine 
from  these  specimens.  "When  preserved  with  the  shell  present,  the  species 
could  undoubtedly  be  recognized  from  its  general  form  and  proportions. 

Horizon. — Residual  chert,  probably  of  Keokuk  limestone. 

Composita  globosa  n.  sp. 
Plate  LXXXII,  Figs.  21-26 

Description. — Shell  small,  subovate  in  outline,  narrowly  truncate  or 
slightly  emarginate  in  front,  usually  a  little  longer  than  wide,  but  some- 
times wider  than  long,  the  greatest  width  near  the  mid-length  of  the 
valve;  the  valves  subequally  convex.  The  dimensions  of  a  nearly  perfect 
specimen  are :  length  of  pedicle  valve  12.5  mm.,  length  of  brachial  valve 
11.1  mm.,  greatest  width  12.1  mm.,  thickness  8.3  mm. 

Pedicle  valve  with  its  greatest  depth  posterior  to  the  middle,  the  sur- 
face curving  abruptly  to  the  cardinal  margin,  and  more  gently  to  the 
lateral  and  anterior  margins ;  the  beak  pointed  and  incurved ;  mesial  sinus 
obsolete  towards  the  beak,  originating  as  a  flattening  of  the  valve  in 
the  umbonal  region  and  continued  to  the  front  margin  as  a  merely  flat- 
tened band  or  as  a  very  shallow  sinus  not  very  sharply  defined  from 
the  lateral  slopes. 

Brachial  valve  with  its  greatest  depth  posterior  to  the  mid- 
dle, the  surface  curving  rather  abruptly  to  the  cardinal  margin 
and  more  gently  to  the  anterior  and  lateral  margins,  not  compressed 
towards  the  cardinal  extremities ;  the  median  portion  of  the  valve  not 
differentiated  from  the  lateral  slopes  posteriorly,  but  anteriorly  it  becomes 
flattened  or  slightly  depressed  in  a  shallow  sinus,  which,  meeting  the 
similar  flattened  band  or  sinus  of  the  opposite  valve,  gives  rise  to  the 
anterior  truncation  or  emargination  of  the  shell. 

Surface  of  both  valves  nearly  smooth,  marked  only  by  faint  lines  of 
growth  which  are  sometimes  crowded  and  more  conspicuous  near  the 
outer  margin  of  the  shell. 

Remarks. — This  is  a  small  species,  rarely  attaining  a  greater  length 
than  15  mm.     It  is  characterized  by  its  more  or  less  globose  form,  nearly 


494  Mlssisxil'lMAN    BBAOHIOPODA 

obsolete  sinus  of  the  pedicle  valve,  and  the  absence  of  a  mesial  fold  in 
the  brachial  valve,  in  place  of  which  the  valve  is  flattened  or  slightly 
sinuous. 
Horizon. — Keokuk  Limestone. 

COMPOSITA  OPPOSITA  (While  ami  Whitfield) 

Plate  LXXXII,  Figs.  11-13 

1862.     Rhynchonella  opposita  While  and  Whitfield,  Proc.  Boston  Soc.  Nat. 
Hist.,  vol.  8,  p.  294. 

Description. — Shell  very  small,  subtriangular  in  outline,  broader  than 
long,  the  greatest  width  near  the  anterior  margin,  the  postero-lateral 
margins  very  long,  nearly  straight  anteriorly,  becoming  slightly  convex 
posteriorly,  meeting  at  the  beak  in  an  angle  of  about  100  degrees,  the 
anterior  margin  trisinuate,  meeting  the  lateral  margins  in  the  acutely 
angular  antero-lateral  extremities  of  the  shell.  The  dimensions  of  the 
holotype  are:  length  of  pedicle  valve  5.5  mm.,  length  of  brachial  valve 
5  mm.,  greatest  width  6  mm.,  thickness  3.2  mm. 

Pedicle  valve  most  convex  posterior  to  the  middle,  the  surface  curving 
abruptly  to  the  cardinal  extremities,  less  abruptly  to  the  antero-lateral 
margins  and  gently  to  the  anterior  margin ;  mesial  sinus  originating  in 
the  umbonal  region,  shallow  and  rather  narrow,  rounded  in  the  bottom, 
not  sharply  defined  laterally,  upon  each  lateral  slope  another  sinus 
similar  to  the  mesial  one,  but  slightly  shallower  and  narrower,  originates 
a  little  in  front  of  the  point  of  origin  of  the  mesial  sinus,  continuing  to 
the  anterior  margin,  these  three  depressions  divide  the  entire  surface 
of  the  valve  anteriorly  into  four  rounded,  subequal  plications ;  the  beak 
incurved,  pierced  by  a  large  foramen  which  encroaches  upon  the  umbonal 
portion  of  the  valve ;  the  delthyrium  filled  by  the  beak  of  the  opposite 
valve. 

Brachial  valve  subequally  convex  with  the  pedicle,  the  greatest  depth 
posterior  to  the  middle,  the  surface  curving  abruptly  to  the  cardinal 
extremities,  less  abruptly  to  the  lateral  margins  anteriorly,  and  more 
gently  to  the  anterior  margin ;  the  surface  of  the  valve  anteriorly  with 
three  shallow  depressions  entirely  similar  to  those  of  the  pedicle  valve 
and  opposite  to  them,  the  presence  of  the  three  depressions  in  each  valve 
producing  the  three  emarginations  in  the  anterior  margin;  the  beak 
strongly  incurved  beneath  that  of  the  opposite  valve. 

Surface  of  both  valves  marked  by  more  or  less  obscure,  regular,  con- 
centric lines  of  growth. 

Remarks. — The  only  example  of  this  species  which  has  come  under  the 
observation  of  the  writer  is  the  holotype  in  the  collection  of  the  American 
Museum  of  Natural  History  in  New  York.  The  original  reference  of  the 
species  to   the   genus  Rhynchonella   is  obviously   incorrect,   the  specimen 


COMPOSITA  495 

clearly  being  an  athyroid  shell  of  the  genus  Composite/,.  The  species 
may  be  easily  distinguished  from  any  other  member  of  this  genus  by  its 
subtriangular  form,  with  its  greatest  breadth  near  the  front  of  the  shell, 
by  the  acutely  angular  antero-lateral  extremities  of  the  shell,  and  by  the 
three  distinct  emarginations  of  the  front. 

The  exact  horizon  of  the  species  can  be  certainly  determined  only  by 
the  collection  of  additional  examples  from  the  type  locality  at  Burlington, 
Iowa.  The  original  definition  gives  the  horizon  as  "Chemung  Group", 
which  would  indicate  Kinderhook.  The  shell  itself  is  from  a  limestone 
and  its  lithologic  characters  would  suggest  that  it  was  collected  from 
the  uppermost  bed  of  the  Kinderhook  at  Burlington. 

Horizon. — Upper  Kinderhook  (?). 

Composita  ?  corpulenta  (Winched) 

Plate  LXXVII,  Figs.  55-59 

1863.     Spirigera  corpulenta  Winched,  Proc.  Acad.  Nat.  Sci.  Phil.,  p.  6. 
1900.     Athyris  corpulenta  Weller,  Trans.  St.  Louis  Acad.  Sci.,  vol.  10,  p.  75, 
pi.  2,  figs.  12-15. 

Description. — Shell  of  medium  size  or  smaller,  subglobose  in  form, 
longer  than  wide,  the  width  and  thickness  subequal,  longitudinally  sub- 
elliptical  in  outline,  the  greatest  width  near  the  mid-length  of  the  shell, 
the  hinge-line  very  short,  the  cardinal  extremities  rounded.  The  dimen- 
sions of  a  nearly  perfect  specimen  are:  length  17  mm.,  width  13.5  mm., 
thickness  13  mm. 

Pedicle  valve  strongly  convex  or  ventricose,  the  greatest  convexity 
near  or  a  little  posterior  to  the  middle,  the  surface  curving  abruptly  in 
all  directions  from  the  point  of  greatest  convexity ;  the  beak  contiguous 
with  that  of  the  opposite  valve,  with  no  indication  of  a  foramen  in  any 
of  the  specimens  examined ;  no  cardinal  area  developed  and  the  characters 
of  the  delthyrium  not  shown  in  any  of  the  specimens ;  mesial  sinus  obscure 
or  obsolete,  when  present  consisting  usually  of  a  mere  flattening  of 
the  surface  along  the  median  line  originating  near  the  middle  of  the  valve, 
which  sometimes  becomes  slightly  concave  anteriorly. 

Brachial  valve  a  little  less  convex  than  the  pedicle,  the  point  of  greatest 
convexity  near  or  posterior  to  the  middle,  the  surface  curving  steeply 
from  the  highest  point  to  the  posterior  and  latei^al  margins,  and  more 
gently  to  the  anterior  margin ;  the  beak  incurved  beneath  that  of  the 
opposite  valve;  the  mesial  fold  not  differentiated. 

Surface  of  both  valves  marked  by  concentric  lines  of  growth  which 
are  crowded  at  intervals. 

Remarks. — The  generic  relations  of  this  species  are  not  clearly  estab- 
lished. The  species  has  been  observed  only  in  a  fine-grained  sandstone  in 
such   condition  of  preservation  that  the   internal   characters   cannot  be 


496  MISSISSIIM'IAN    BBACHIOPODA 

determined.    In  its  external  characters  the  species  most  closely  resembles 

the  Silurian  Eindella  wmbonata  (Bill.),  from  Anticosti,  hut  that  genus  has 
not  been  recognized  outside  of  Anticosti  and  it  is  not  likely  that  this 
Kinderhook  form  is  congeneric  with  thai  very  much  earlier  species,  es- 
pecially in  view  of  the  fact  thai  the  genus  has  not  been  recognized  any- 
where in  the  intervening  faunas.  In  one  specimen  observed,  the  posterior 
portion  of  the  shell  is  in  the  condition  of  an  internal  cast,  and  the  median 
portion  of  the  brachial  valve  appears  as  a  ridge  running  to  a  point  under 
the  beak  of  the  opposite  valve,  this  condition  being  entirely  similar  to 
thai  in  the  internal  easts  of  undoubted  athyroid  shells,  this  ridge  being 
the  cast  of  the  canal  which  passes  to  (he  perforation  through  the  hinge- 
plate.  The  original  reference  of  the  species  to  the  genus  Spirigera  was 
essentially  a  reference  to  Athyris,  hut  the  contour  of  the  shell  is  more  nearly 
like  members  of  the  genus  Composita,  except  in  the  close  approximation  of 
the  beaks  of  the  two  valves,  and  the  species  is  therefore  placed  in  that  genus. 
Horizon. — Chonopectus  sandstone  of  the  Kinderhook. 


GENERAL   INDEX 


Italics  refer  to  synonyms.     Roman  numerals  refer  to  plate  numbers.     Arabic 
nu  merals  refer  to  pages. 

A 

Acambona,   White   448 

A cambona  ?  osagcnsis 439 

A.  prima  White 449,  LXXVI 

Acanthospira,   n.   gen 418 

Acanthospira  aciculifera   (Rowley) 418,  XXXV 

Allorhynchus,   Weller 197 

Allorhynchus  acutiplicatum,  n.  sp 201,  XXIV 

A.  heteropsis     (Winchell) 197,  XXIV 

A.  maera  (Hall) .- 199,  XXV 

Ambocoelia,  Hall  423 

Amboccelia  levicula  Rowley 426,  LXXVII 

A  minuta  White  423,  LXXVII 

A.  parva    Weller   424,  LXXVII 

A.  unionensis   n.   sp 425,  LXXVII 

.1 .  (Spirifer?)   minuta. 423 

Athyridas  464 

Athyris,  McCoy 464 

Athyris  ashlandensis 465 

A.  corpuh'nta    495 

A.  crassicardinalis  White 471,  LXXVII 

A.  densa  Hall  469,  LXXVII 

A.  hannibalensis    (Swallow) 467,  LXXVIII 

A.  hirsuta    479 

A.  incrassatus  465,  475,  477 

A.  lamellosa  (Leveill£) 465,  LXXVIII 

A .  obmaxima 475 

A.  obvia   482 

A.  papilioniformis  McChesney  468,  LXXVIII 

A.  parvirostra  481 

A.  planosulcata  ?  481 

A.  proutii 471 

A .  spiriferoides    468 

A.  sublamellosa   482 

A.  subquadrata  486,  489 

A.  tenuilineata  478 

A .  trinucleus  486 

Atremata    33 

Atrypa,  Dalman 284 

Atrypa  infrequens  n.  sp 285,  XXXV 

A.  spinosa  285 

Atrypidae 284 

B 

Drachythyris,  McCoy 370 

Brachythyris  altonensis  n.  sp 379,  LIX 

B.  burlingtonensis   n.   sp 371,  LIII,  LXXXIII 

B.  chouteauensis  Weller 373,  LVII 

B.  fernglenensis   Weller 372,  LII 

B.  gurleyi  n.  sp 377,  LVIII 

B.  peculiaris   (Shumard) 381,  LVII,  LVIII,  LXXXIII 

B.  semiplicata   (Hall) 380,  LIX 

B.  subcardiiformis  (Hall) 376,  LX 

B.  suborbicularis    (Hall) 374,  LXI,  LXII 


198  GENERAL   INDEX 

Brewerville  formation  24 

Burlington,  Iowa,  Section  at 13 

Burlington  limestone      16 

C 

Camarophorella,  Hall  and  Clarke 458 

Camarophorella  lenticularis  (White  and  Whitfield) 459,  LXXX1I 

C.  missouriensis   (Winchell) 460,  LXXXII 

Camarophoria,  King 169 

Camarophoria  arctirostrata 215 

C.  bisinuata    (Rowley) 172,  XXIII 

< '  caput-testudinls  206 

C.  explanata    (McChesney) 173,  XXIII 

C.  hamburgensis    Weller 170,  XXIII 

C.  occidentalis  233 

C.  ringens  218 

C.  subcuncata    214 

C.  subtrigona  218 

0.  ivortheni    203 

Camarotoechia,  Hall  and  Clarke 175 

Camarotoechia  chouteauensis  Weller 176,  XXIV 

C.  elegantula    Rowley 177,  XXIV 

C.  grosvenori     (Hall) 183,  XXIV 

C.  (?)   heteropsis  197 

C.  mutata   (Hall) 181,  XXIV 

C.  persinuata  233 

C.  subglobosa    n.    sp 180,  XXIV 

C.  tuta    (Miller) 179,  XXIV 

Centronella,   Billings   241 

Centronella  allei  252 

C.  crassicardinalis    469 

C.  ?  emaciata  Rowley 242,  XXX 

C.  louisianensis  n.  sp 241,  XXX 

Centronellidae    241 

Centronelloidea   n.    gen 246 

Centronelloidea  rowleyi    (Worthen) 247,  XXXI 

Chester  group  23 

Chonetes,  Fischer  de  Waldheim 78 

Chonetes  chesterensis  n.  sp 83,  VIII 

C.  burlingtonensis  Weller  93,  VIII 

C.  fischeri  96 

C.  geniculatus   White   92,  VIII 

C.  glenparkensis  Weller  87,  VIII 

C.  gregarius  Weller  91,  VIII 

C.  illinoisensis    Worthen 81,  VIII 

G.  illinoisensis    79 

C.  logani  Norwood  and  Pratten 84,  VIII 

C.  logani  81 

C.  missouriensis   n.   sp 82,  VIII 

C.  multicosta  Winchell  79,  VIII 

C.  ornatus   Shumard  86,  VIII 

C.  planumbonus  Meek  and  Worthen 94,  VIII 

G.  shumardiana    89 

C.  shumardanus    DeKoninck 89,  VIII 

Chonopectus,  Hall  and  Clarke 95 

Chonopectus  fischeri   (Norwood  and  Pratten) 96,  VIII,  LXXXIII 

Classification  of  the  Mississippian   System 12 

Gleiothyris   hirsuta :. 478,  479,  483 

C.  incrassata   475 

C.     ■  prouti  471 

C.  royssi    473 

Cliothyridina,   Buckman   472 


GENERAL   INDEX  499 

Cliothyridina  glenparkensis  n.  sp 473,  LXXVIII 

C.  hirsuta  (Hall) 479,  LXXX 

C.  incrassata    (Hall) 477,  LXXIX 

C.  lenticularis   n.   sp 480,  LXXX 

C.  obmaxima    (McChesney)  475,  LXXIX 

C.  parvirostris    (Meek  and  Worthen) 481,  LXXVIII,  LXXX 

C.  prouti    (Swallow) 474,  LXXIX 

C.  sublamellosa     (Hall) 482,  LXXX 

C.  tenuilineata    (Rowley) 478,  LXXX 

Cliothyris  crassicardinalis 471 

C.  hirsuta    479 

C.  roysii  479,  483 

Clore  formation  29 

Composita,    Brown    484 

Composita  ?  corpulenta   (Wlnchell) 495,  LXXVII 

C.  globosa  n.  sp 493,  LXXXII 

C.  laevis  n.  sp 491,  LXXXII 

C.  lewisensis  n.   sp 488,  LXXXI 

C.  opposita    (White   and   Whitfield) 494,  LXXXII 

C.  pentagonia  n.  sp 492,  LXXXII 

C.  subquadrata     (Hall) 489,  LXXXI 

C.  sulcata  n.  sp 490,  LXXXI 

C  trinuclea    (Hall)  486,  LXXXI 

Cranaena,  Hall  and  Clarke 248 

Cranaena  ?  allei  (Winchell) 252,  XXXIV 

C  globosa    n.    sp 249,  XXXIV 

C.  sulcata  n.  sp 251,  XXXIV 

Crania,   Retzius   43 

C.  blairi    Miller   46,  I 

C.  chesterensis   Miller  and   Gurley 45,  I 

C.  dodgei   Rowley 44,  I 

C  lasvis  Keyes  47,  I 

C  missouriensis  Weller 43,  I 

C.  reposita  White  44,  I 

C.  rowleyi   Gurley  46,  I 

C.  spiculata  Rowley  47,  I 

Craniidae   43 

Cryptonella  ?  sp.  indet 283 

Cyrtia,  Dalman  382 

Cyrtia  acutirostris 286 

C.  inexpectans    n.    sp 383,  LXIII 

Cyrtina,  Davidson 286 

C.  acutirostris  (Shumard) 286,  XXXV 

C.  burlingtonensis  Rowley  288,  XXXV 

C  neogenes  Hall   and   Clarke 289,  XXXV 

C.  sp.  ? 289 

D 

Delthyris,  Dalman  300 

Delthyris   clarksvillensis    (Winchell) 301,  XXXVI 

D.  missouriensis  Weller  302,  XXXVI 

D.  novamexicana    (Miller) 304,  XXXVI 

D.  similis  n.  sp 305,  XXXVI 

D.  suborbicularis   Weller   303,  XXXVI 

Derbya  ( f )  costatula 57 

D.         kaskaskiensis    77 

D.  keokuk    75 

D.  ruffinosa    71 

Diaphragmus,  Girty  135 

Diaphragmus  elegans   (Norwood  and  Pratten) 136,  XII 

Dielasma,   King   256 


500  GENERAL    INDEX 

Dielasma  allei  252 

I).  arkansanuni,  n.  sp  ........  269,  XXXI 

I).  burlingtonensis    (White) 261,  XXXI 

D.  builiiiiilini,  ns is       249 

1>.  chouteauensls  n.  sp 257,  XXXII 

D.  fernglensis   Weller  259,  XXXIII 

1).  formosum    (Hall) 265,  XXX111 

l>.  formosa   249,  256,  262 

/>.  gorbyi    262 

ii  Ulinoisensis  n.  sp  267,  XXXIII 

I).  inflata  n.  sp 264,  XXXII 

/'.  obovata    265 

D.  osceolensis  n.  sp         260,  XXXIII 

n.  (.')  pediculus  244 

l>.  :  rowleyi      247 

l)  aubspatulatum  n.  sp  270,  XXXIII 

I).  Bhumardanum    (Miller)  268,  xxxi 

I).  sinuata  n.  sp  262,  XXXI 

D.  turgida  251,  262,   264,   273,   275,   278 

i>.  turgida  var.  elongata 278 

Dielasmella,    Weller  279 

Dielasmella  calhounensis  n.  sp 281,  XXXI 

D.  compressa  Weller  280,  XXX 

Dielasmoides,  Weller  253 

Dielasmoidea  bisinuata  Weller 254,  XXXI 

Discina  capax  39 

/'.  kcokuk    41 

I).  sa  hi  psoni    40 

/'.  varsovlensis 41 

Discinidae   39 


Echinoconchus   n.   gen 138 

Echinoconchus     alternatus   (Norwood  and  Pratten) 138,  XVII 

E.  biseriatus     (Hall) 141,  XVII 

E.  genevievensis  n.  sp 140,  XVIII 

E.  morbillianus  (Winchell) 142,  XVIII 

Eumetria,  Hall  437 

Eumetria  acuticosta  n.  sp 447,  LXXVI 

E.  altirostris    (White)  438,  LXXVI 

E.  costata    (Hall) 445,  LXXVI 

E.  m  a  re  in  442,  444 

E.  osagensis    (Swallow) 439,  LXXVI 

E  perstrialis  Rowley  441,  LXXVI 

E.  vera    (Hall)  444,  LXXVI 

E.  vera  var.  costata 445 

E.  verneuiliana    (Hall) 442,  LXXVI 

Eunella   compressa  280 


Girtyella,  Weller  271 

Girtyella  brevilobata    (Swallow) 278,  XXXIV 

G.                cedarensis   n.   sp 272,  XXXIV 

G.                indianensis   (Girty) 275,  XXXIV 

G                intermedia  n.  sp 276,  XXXIV 

G.                turgida     (Hall) 273,  XXXIV 

Glossina  Phillips  37 

Glossina  lineolata    (Rowley) 38,  I 

G.               sedaliensis    (Miller) 37,  I 


GENERAL    INDEX  501 

H 

Hamburg,  Illinois,  Section  at 14 

Hamburgia,  Weller  282 

Hamburgia  typa  Weller 283,  XXXI 

II  art  tin  a  brevilobata  278 

H.             indianensis   275 

Hemipronites  inequalis  6 1 

Hustedia,  Hall  451 

Hustedia  circularis   (Miller) 451,  LXXVI 

J 

Jefferson  County,  Missouri,  Section  at 15 

Jonesboro,  Illinois,  Section  3%  miles  northwest  of 15 


Keokuk  limestone  17 

Kinderhook  group  13 

Kinderhook,    Illinois,    Section   at 13 

L 

Leiorhynchus   booncnsis  195 

L.  greeneanum  185 

Lepta?na,  Dalman    48 

Lepta?na  analoga  (Phillips) 49,  IT 

L  convexa  n.  sp 52,  II 

L.  rhomboidalis  49,  52 

Lingula,  Bruguiere  33 

Lingula  crawfordsvillensis  262 

L.  gorbyi   Miller  35,  I 

L.  halli  White  35,  I 

L.  indianensis  Miller  and  Gurley 37,  I 

L.  lincolata  38 

L  louisianensis  n.  sp 34,  I 

L.  membranacea    Winchell    33,  I 

L.  sedaliensis 37 

L  varsoviensis  Worthen  36,  I 

Lingulidas  _  33 

Jjingulidiscina  batesvillensis  42 

Liorhynchus,  Hall  185 

Liorhynchus  greenianum    (Ulrich) 185,  XXV 

M 

Martinia,   McCoy   420 

Martinia  contracta  (Meek  and  Worthen) 420,  LXXV 

M.  sulcata    n.    sp 422,  LXXV 

Menard  formation  28 

Meramec   group   19 

Meristellidse 453 

Missouri    localities,   Sections   at 14 

Missouri,   Sections   in   southwestern 14 

N 

Neotremata    39 

Nucleospira,  Hall  453 

Nucleospira  barrisi   White 455,  LXXXII 

.Y.  barrisi  454 

NT.  minima  Weller  456,  LXXXII 

N.  obesa  Rowley 457,  LXXXII 

N.  rowleyi   n.    sp 454,  LXXXII 


<r>02  GENERAL   INDEX 

O 

Okaw  formation 27 

Orbiculoidea,  d'Orbigny  39 

Orbiculoidea  batesvillensis  Weller 42,  I 

O.  capax    (White)    39,  I 

O.  keokuk    (Gurley)    41,  I 

O.  sampsoni    (Miller)    40,  I 

O.  varsoviensis   (Worthen) 41,  I 

Orthidae 147 

Orthis  burlingtoncnsis  ...  149 

0.  cooperensis 160 

o.         erenistria  75 

O.  dubia  160 

0.  incqualis  61 

0.  kaskaskicnsis   77 

O.  krokuk    75 

O.  michclini    151 

O.  michclini  var.   burlingtoncnsis 149 

O.  missouricnsis    148 

0.  rcsupinata    .167 

0.  subclliptica    162 

0.  swallovi  167 

O.  thcimei  155 

O.  umbraculum    70 

O.  (Rhipidomclla)    burlingtonensis  149 

0.  (R.  )    Owcni  151 

Orthotetes,  Fischer  de  Waldheim 74 

Orthotetes    kaskaskiensis    (McChesney) 77,  VI 

O.  keokuk     (Hall) 75,  VII 

Orthothctcs  inuqualis  61 

O.  inflatus   59 

O.  lens    55 

0.  minutus  70,  71 

O.  rubra 54,  56 

O-  sp    65 

Osage   group   16 

P 

Paint  Creek  formation  26 

Palestine  formation 29 

Paraphorhynchus  elongatum  191 

P.  gibbosum  221 

P.  ovatum  208 

P.  striatocostatum   189 

P.  transvcrsum  188 

Paryphorhynchus,  Weller  187 

Paryphorhynchus  elongatum  Weller 191,  XXVI 

P.  striaticostatum  (Meek  and  Worthen)  189,  XXVI 

P.  transversum  Weller  188,  XXVI 

Pentamerids  169 

Pentamerus  lenticularis  459 

Plectambonites  rhomboidalis  49 

Producta  analoga  49 

P.  arcuata  107 

P.  conccntrica  98 

P.  parvula 128 

P  cooperensis  98 

Productidae    78 

Productella,  Hall  97 

Productclla  arcuata 107 

P.  concentrica    (Hall) 98,  XIX 

P.  cooperensis    98 

n.  nummularis    (Winchell) 101,  XIX 

P.  pyxidata  Hall  100,  XIX 

r>  shumard  iana    98 

P.  subltevis  n.  sp 102,    LXXXIII 


GENERAL   INDEX  503 

Productus,   Sowerby   103 

Productus  alternatus  138 

P.  altonensis   Norwood   and    Pratten 124,  X 

P.  arcuatus  Hall 107,  XIII 

P.  biseriatus  141 

P.  blairi  Miller  110,  XIV 

P.  blairi    108 

P.  burlingtonensis   Hall    104,  IX 

P.  burlingtonensis 124 

P.  1 1  stricnsis  136 

P.  eoncentricus   98 

P.  eooperensis   98 

P.  cora'formis  132 

P.  crawfordsvillensis  n.  sp 116,  XII 

P.  curtirostris  Winchell  130,  XIV 

P.  elegans  136 

P.  fasciculatus    136 

P.  fentonensis  117 

P.  fernglenensis  Weller  106,  IX 

P.  ftm  b  riatus   141 

P.  flemingi  var.  burlingtonensis 104 

P.  flexistria    136 

P.  gallatinensis  124 

P.  (/radatus  138 

P.  indianensis  Hall  131,  XVIII,  LXXXIII 

P.  inflatus   McChesney  Ill,  X 

P.  laevicostus 132 

P.  raagnus  Meek  and  Worthen 117,  XV 

P.  magnus    116 

P.  marginicinctus  Prout 127,  XIII 

P.  mesialis  Hall  112,  X,  LXXXIII 

P.  mesicostalis  n.  sp 114,  XI 

P.  morbillianus  142 

P.  ovatus    Hall    132,  XVI 

P.  parvulus  Winchell   128,  XIV 

P.  parvus  Meek  and  Worthen 121,  XVI 

P.  pileiformis  132 

P.  prattcnianus  132 

P.  pyxidatus    100 

P.  sampsoni  Weller  129,  XIII 

P.  scitulus  Meek  and  Worthen 120,  XIII 

P.  sedaliensis  n.  sp 108,  XIV 

P.  semireticulatus 114,  122,  130 

P.  setigerus   Hall   122,  XII 

P.  setigerus  ?  var.  keokuk 114 

P.  shumardianus    98,  100 

P.  tenuicostus  Hall 119,  X,  XI 

P.  viminalis  White  114,  XI 

P.  vittatus  _ 138 

P.  wortheni   Hall   126,  XIII 

Protremata    48 

Pseudosyrinx  n.  gen 404 

Pseudosyrinx  gigas  n.  sp 410,  LXVI 

P.  keokuk  n.  sp 408,  LXVI,  LXVII 

P.  missouriensis   n.   sp 406,  LXV,  LXVI 

P.  sampsoni  Weller  405,  LXVII 

Ptychospira,   Hall    435 

Ptychospira  sexplicata   (White  and  Whitfield) 435,  LXXVI 

Pugnax,  Hall  and  Clarke 202 

Pugnax  explanatws  173 

P.  greenianus 185 

P.  grosvenori    183 

P.  missouriensis  188,  189,  237 

P.  mutata  181 

P.  ottumwa    193 


.r>()4  GENERAL    INDEX 

P.  quadrirostris  Beede  204,  XXV 

P.  striatocostata 189 

P.  striatocostata  var.   ' 188 

1'.  worthoni   (Hall)  203,  XXV 

Pugnoidea,  Weller  192 

Pugnoides  boonensis  (Shuniard)  195,  XXV 

P.  ottumwa  (White)   193,  XXV 

R 

Renault    formation  24 

Reticularia,  McCoy         427 

Reticularia  cooperensis    (Swallow) 428,  LXXV 

R.  pseudolineata    (Hall)    429.  LXXIV.  LXXV 

R.  pseudolineata  f  432 

K.  salemensis  n.  sp 433,  LXXV 

R.  setigera   (Hall)   431,  LXXIV 

Retzia  circularis  451 

R.  osagensis   439 

R.  plica ta  435 

R.  .'  raricosta  s  435 

K.  sexplicata  435 

R.         vera  444 

/>'.  vera  var.  costata 445 

R.  verneuiliana   442 

R.  (Acambona  .")   altirostris 438 

Rhipidomella,   Oehlert  147 

Rhipidomella  burlingtonensis   (Hall) 149,  XXI,  LXXXIII 

R.  burlingtonensis  155 

R.  diminutiva   Rowley   153,  XX 

R.  dubia    (Hall) 160,  XX,  LXXXIII 

R.  jerseyensis  n.  sp 157,  XX 

R.  michclinia  157 

R.  missouriensis   (Swallow) 148,  XX 

R.  oweni  Hall  and  Clarke 151,  XXI 

R.  tenuicostata   n.   sp 158,  XX 

R.  thiemei    (White)    155,  XXI 

Rhynchonclla  arctirostrata 215 

R.  boonensis    195 

R.  caput-testudinis  206 

R.  cooperensis  235 

R.  explanata    173 

B.  greeniana 185 

R.  grosvenori  183 

R.  heteropsis  197 

R.  macra  199 

R.  missouriensis  189,  222,  224 

R.  mutata  181 

R.  obscura-plicata    224 

R.  opposita  494 

R.  otturniva-  193 

R.  parvini  218 

R.  perrostellata  214 

R.  persinuata  233 

R.  pustulosa  230 

R.  ricinula   199 

R.  striatocostata    189 

R.  subcuneata   214 

R.  subtrigona    218 

R.  tuta  179 

R.  wortheni   203 

R.  sp.   ?  206,  211 

R.  (Eatonia)    obsolens  224 

Rynchonellidaa    175 

Rhynehopora,  King  227 


GENERAL   INDEX  505 

Rhvnchopora  beecheri  Greger 232,  XXIX 

R.  ?  cooperensis    (Shumard) 235,  XXX 

R.  hamburgensis   Weller 228,  XXIX 

R.  ?  perryensis  n.  sp 239,  XXV 

R.  persinuata    (Winchell) 233,  XXX 

R.  pustulosa   (White)   230,  XXIV,  XXIX 

R.  ?  rowleyi  n.  sp ...• 237,  XXX 

Rliynchospirid;e      435 

Rhynchotetra,  Weller  205 

Khynehotetra  caput-testudinis  (White) 206,  XXVII 

R.  elongatum  n.   sp 209,  XXVIII 

R.  gibbosum    (Greger) 211,  XXVII 

R.  missouriensis  n.   sp 210,  XXVIII 

R.  ovatum    (Greger)    208,  XXVII 

Rowleyella,  Weller   462 

Rowleyella  fabulites   (Rowley) 463,  LXXXII 

Ruma  formation 26 

S 

Ste.   Genevieve   limestone 21 

St.    Louis   limestone 20 

Salem  limestone  19 

Schellweinella,  Thomas  59 

Schellwienella  alternata  n.  sp 66,  IV 

S.  burlingtonensis  n.  sp 67,  IV 

S.  chouteauensis  n.   sp 67,  III 

S.  crenulicostata  n.  sp 63,  III 

S  inaequalis   (Hall)   61,  III 

S.  inriata   (White  and  Whitfield) 59,  IV,  LXXXIII 

S.  planumbona  n.  sp 65,  III 

Schizophoria,   King  161 

Schizophoria  chouteauensis  n.   sp 163,  XXIII 

S.  poststriatula   n.   sp 165,  XXII 

S.  sedaliensis  n.  sp 164,  XXI 

S.  subelliptica    (White  and  Whitfield) 162,  XXIII 

S.  swallovi    (Hall)   167,  XXII 

8.  Swallovi  165 

Schuchertella,  Girty  53 

Schuchertella  costatula   (Hall  and  Clarke) 57,  II 

S.  fernglenensis  n.   sp 54,  III 

S.  lens   (White)   55,  III 

S.  rubra  Weller  56,  III 

Section  at  Burlington,   Iowa 13 

Section  at  Hamburg,  Illinois 14 

Section  in  Jefferson  County,  Missouri 15 

Section  3%  miles  northwest  of  Jonesboro,  Illinois 15 

Section  at  Kinderhook,  Illinois 13 

Sections  at  Missouri  localities 14 

Section  in  southwestern  Missouri 14 

Section  at  Warsaw,  Illinois 18 

Selenella,  Hall   243 

Selenella  pediculus   (Rowley) 244,  XXX 

Scminula  bisinuata  172 

8.  buckleyi    460 

8.  subquadrata  486 

8,  trinuclea  486 

Shumardella,  Weller  221 

Shumardella  missouriensis   (Shumard) 222,  XXV 

S.  obsolens    (Hall)    224,  XXVI 

8.  obsolescent  224 

Spirifer,   Sowerby   307 

Spirifer  attenuatus  350 

S.  bifurcatus  Hall      346,  XLVII 

S.  biplicatus    Hall    320,  XXXIX 


506 


GENERAL    INDKX 


8.  biplicatus    .  ...  323 

S.  blpllcoides  a.  sp  323,  XXXIX 

S.  breckenridgensis  n.  sp 342,  xliv 

calvini  n.  sp  368,  LIV 

S.  carlnatus  Rowley  336,  XLIV 

8.  carteri .       .   .  399 

8.  centronatus  323 

8.  ehouteauensis  373 

8.  cooperensis  380,  428 

S.  crawfordsvillensis   n.   sp  338,  XLVII 

8.  r.rh  mint  its  ;jS(i' 

8.  fastigatus  366 

8.  fernglenensis  372 

S.  floydensis  n.  sp  351,  XLIX 

S.  forbesi  Norwood  and  Pratten 331,  XLII,  XLIII,  LXXXIII 

8.  glaber  420 

8.  glaber  var.  contractus  420 

S.  gregeri   n.   sp 359,  LV 

S.  grimesi  Hall  361,  LI,  LII,  LIII 

<S.  hirtus   428 

S.  imbrex   Hall  334,  XLIII 

S.  incertus  Hall 335,  XLI 

S.  increbescens  Hall  343',  XLV1 

S.  indianensls   n.    sp 352,  L 

S.  insculptus   Rowley   324^  XL 

S.  jeffersonensis  Weller  369^  XLII 

S.  keokuk  Hall  350,  XLIX 

8.  keokuk  340 

8.  keokuk  var 346 

S.  la  m  ellosus  465 

S.  lateralis  Hall  330,  XLIII 

S.  lateralis  var.  delieatus 330 

S.  latior  Swallow  316,  XXXVIII 

S.  legrandensis   n.   sp 326,  XL 

S.  leidyi  Norwood  and  Pratten 345,  XLVII 

8.  leidyi  var.  merimaeensis 346 

S.  littoni   Swallow  348,  L 

S.  logani  Hall  363,  LVI,  LVII 

S.  louisianensis  Rowley  322,  XL 

S.  maplensis  n.  sp 357,  LI 

S.  marionensis  Shumard  308,  XXXVII 

S.  marionensis    314,  317 

S.  marshallensis  n.   sp 349,  L 

S.  missouriensis   Swallow  319,  XXXIX 

S.  montgomeryensis  n.  sp 367,  LV 

S.  mortonanus  Miller  366,  LVIII,  LIX 

S:  mundulus  Rowley 333,  XLIV 

S.  neglectus    415 

S.  norwoodana 295 

S.  osagensis   Swallow  314,  XXXVII 

S.  peculiaris  371,  381 

S.  pellaensis  n.  sp 340,  XLV 

S.  pikensis   Rowley  312,  XXXVIII 

S.  platynotus  n.   sp 317,  XXXIX 

8.  plenus  412 

8.  pseudolineatus  429 

8.  rockymontana    340 

S.  rostellatus  Hall  353,  XLVIII 

S.  rowleyi  n.  sp 360,  LIII,  LIV 

8.  schucherti  416 

8.  semiplicata   380 

S.  setigerus    431 

S.  shepardi  n.  sp 313,  XXXVIII 

S.  solidirostris    292 

S.  spinosus  299 


GENERAL   INDEX  507 

S.  striatiformis  Meek  364,  XLVIII 

S.  suba?qualis    Hall    327,  XLIII 

8.  s libit  qiialis  328 

8-  subi  iirdiiformis   376 

S.  subcuspidatus  401 

8.  subellipticus  294 

8.  suborbieularis    374 

8.  subrotundutus    356 

S.  subrotundus  n.  nom 356,  L 

S.  tenuicostatus  Hall  328,  XLII 

S.  tenuimarginatus   Hall  355,  XLVIII 

8.  textus   _ 399 

8.  transversa  297 

S.  vernonensis  Swallow  310,  XXXVII 

S.  washingtonensis  n.  sp 339,  XLIV 

8.  (Cyrtia  ?)   hannibalensis 388 

S.  (Martinia)   contractus  420 

S.  (Trigonotreta)   striatiformis  364 

Spirifera  aciculifera  418 

S.  contracta  420 

S.  cooperensis   428 

8.  glabra  var.  contracta .-. 420 

8.  grimesi  361 

S.  hirta  428 

S.  logani   363 

S.  mortonana  366 

S.  nova  mcxicana  304 

8.  peculiaris    381 

S.  pscudolineata  429 

S.  rostellatus  353 

S.  temeraria  474 

S.  tenuimarginatus    355 

S.  (Martinia)   contracta  420 

Spiriferella,    Tschernyshew    412 

Spiriferella  latior  n.  sp 414,  LXIII 

S.  neglecta    (Hall)    415,  LXIV,   LXV 

S.  plena   (Hall)    412,  LXIII,  LXIV 

S  ?  schucherti  (Rowley) 416,  XXXV 

Spiriferidae    J 286 

Spiriferina,  d'Orblgny  291 

Spiriferina    aciculifera  _  418 

S.  clarksvillensis    301 

8.  magnicostatus    304 

S.  norwoodana   (Hall)    295,  XXXVI 

S.  salemensis  n.  sp 296,  XXXVI 

S.  solidirostris  White  292,  XXXVI 

S.  subelliptica     (McChesney) 294,  XXXVI 

S.  subtexta  White   291,  XXXVI 

S.  spinosa   (Norwood  and  Pratten) 299,  XXXV 

S.  transversa    (McChesney)    297,  XXXV 

8pirigera  amerieana  482 

S.  elintonensis   482 

8.  corpulenta    495 

S.  hannibalensis    467 

S.  hirsuta    479 

S.  missouriensis    : 460 

8.  obmaxima    475 

8.  pectinifera   475 

S.  proutii  475 

Streptorhynchus,  King 68 

8treptorhynchus  aequivalvis  61 

8.  equivalvis  61 

S.  inequalis  61 

S.  inflatus    59 

-S.  keokuk 75 


5<  18 


GENERAL    IN'DKX 


g, 
S. 
S. 
S. 
S. 
8. 
8. 


h  ns  

ininutum  (Cumlngs) 
ruginosum  (Hall  and  Clar 
tenulcostatum   n.  sp 
ulrichi  Hall  and  Clarke 
williamsi  

(OrtJiis)    K  iti  lira  i  tilum  


ke) 


Strophalosia,    King 

Strophalosia  beecher)   Kowley 

S.  cymbula   Hall  and  Clarke 

S.  keokuk   Beecher 

8.  .'  nummularis 

S.  scintilla    Beecher 

Strophomena  rhomboidalis         

S.  rhoitihoiihilis  vur.  analoga.. 

Strophomenidae 
Syringothyris,    Winchell 
Syringothyris  bushbergensis  n.  sp 


8. 

S. 

s. 
s 
s. 
s. 

s. 

s. 

8. 
8. 
S. 

S. 

s. 
s. 


carteri 

cuspidatus   Martin 
eztenuatus  (Hall) 
halli  Winchell 
hannibalensis  (Swallow  ) 

missouri   Hall   

newarkensis  n.  sp 

platypleurus  n.  sp  

plena    

sa  in  jisoni  

solidirostris   n.   sp 
subcuspidatus   (  Hall ) 
textus    (Hall) 
typus  Winchell      


55 

70,  VI 

71,  V 
69,  IV 
73,  II 
70 

70 
143 

146,  XIX 
145,  XIX 
145,  XVIII 
101 
144.  XVIII 

49 

49 

48 
384 

391,  LXXIII 
388,  395,  406 
LXXIII 
386,  LXXII 
390,  LXXII 
388,  LXVIII 

393,  LXX 

394,  LXVIII 
397,  LXXII 
412 

405 

403,  LXX 

401,  LXXI 

399,  LXIX,  LXX,  LXXI 

395,  LXIX 


Telotremata  175 

Terebratula  arvuata  175 

T.  brevilobata  278 

T.  burlingtonensis  261 

T.  fabulites  463 

T.  formosa     265 

T.  rowleyi   247 

T.  serpentaria  ?  442 

T  shumardana 268 

T.  trinuclea  486 

T.  turgida   273,  275 

Terebratulids  246 

Tetracamera,   Weller   212 

Tetracamera  arctirostrata    (Swallow) 215,  XXVIII 

T.  missouriensis  n.  sp 216,  XXVIII 

T.  subcuneata  (Hall)  214 

T.  subtrigona  (Meek  and  Worthen) 218,  XXIX 

Trigeria,    Bayle   245 

Trigeria  (?)   curriei  Rowley 245,  XXX 

W 

Warsaw   formation   17 

Warsaw,  Illinois,  Section  at 18 

Wilsonia  grosvcnori  183 


Yankeetown    formation 


25 


■        • 


* 


mm 


■ 


■  ■  ■ 


Be 

■ 

■ 
■  ■ 

■Ml      Hi 
Ira  -w 

H 

•  I  ■ 


